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          George Wingfield, appellant, v. Hill Brothers
                 Transportation, Inc., appellee.
                                    ___ N.W.2d ___

                         Filed May 16, 2014.     No. S-13-716.

 1.	 Workers’ Compensation: Appeal and Error. Pursuant to Neb. Rev. Stat.
      § 48-185 (Cum. Supp. 2012), an appellate court may modify, reverse, or set aside
      a Workers’ Compensation Court decision only when (1) the compensation court
      acted without or in excess of its powers; (2) the judgment, order, or award was
      procured by fraud; (3) there is not sufficient competent evidence in the record to
      warrant the making of the order, judgment, or award; or (4) the findings of fact
      by the compensation court did not support the order or award.
 2.	 ____: ____. An appellate court is obligated in workers’ compensation cases to
      make its own determinations as to questions of law.
 3.	 ____: ____. The issue in regard to causation of an injury or disability is one
      for determination by the fact finder, whose findings will not be set aside unless
      clearly wrong.
 4.	 Workers’ Compensation. In workers’ compensation cases, the heart injury
      causation issue consists of two elements: (1) legal causation and (2) medi-
      cal causation.
 5.	 Workers’ Compensation: Proof. When a preexisting disease or condition is
      present, the Nebraska Supreme Court has adopted the following test for legal
      causation: An exertion- or stress-caused heart injury to which the claimant’s pre-
      existing heart disease or condition contributes is compensable only if the claimant
      shows that the exertion or stress encountered during employment is greater than
      that experienced during the ordinary nonemployment life of the employee or any
      other person.
  6.	 ____: ____. If it is claimed that an injury was the result of stress or exertion in
      the employment, medical causation is established by a showing by a preponder-
      ance of the evidence that the employment contributed in some material and sub-
      stantial degree to cause the injury.
  7.	 ____: ____. In a workers’ compensation case involving a preexisting condition,
      the claimant must prove by a preponderance of evidence that the claimed injury
      or disability was caused by the claimant’s employment and is not merely the pro-
      gression of a condition present before the employment-related incident alleged as
      the cause of the disability.
 8.	 Workers’ Compensation. A claimant in a workers’ compensation case involving
      a preexisting condition may recover when an injury, arising out of and in the
      course of employment, combines with a preexisting condition to produce disabil-
      ity, notwithstanding that in the absence of the preexisting condition, no disability
      would have resulted.
 9.	 ____. When a workers’ compensation claimant has suffered a heart attack, the
      foremost and essential problem is causation, that is, whether the employment
      caused an employee’s injury or death from a heart attack.
                       Nebraska Advance Sheets
	                     WINGFIELD v. HILL BROS. TRANSP.	175
	                            Cite as 288 Neb. 174

10.	 ____. The single judge of the Workers’ Compensation Court is the sole judge of
     the credibility of the witnesses and the weight to be given their testimony, even
     where the issue is not one of live testimonial credibility.

  Appeal from the Workers’ Compensation Court: John R.
Hoffert, Judge. Affirmed.
  Stacy L. Morris, of Lamson, Dugan & Murray, L.L.P., for
appellant.
  Caroline M. Westerhold, of Baylor, Evnen, Curtiss, Grimit
& Witt, L.L.P., for appellee.
  Heavican, C.J., Wright, Connolly, Stephan, McCormack,
Miller-Lerman, and Cassel, JJ.
    Cassel, J.
                        INTRODUCTION
   This case requires us to decide whether the causation stan-
dard applicable to workers’ compensation claims involving
injury from heart attack was properly extended to an episode
of deep vein thrombosis and pulmonary embolism. In heart
attack cases, a claimant is required to prove both legal and
medical causation. The compensation court applied this split
test of causation and dismissed for failure to establish the
medical cause prong. The split test arises from the difficulties
in attributing the cause of a heart attack to the claimant’s work.
Because deep vein thrombosis and pulmonary embolism pre­
sent these same difficulties and are similar in origin to a heart
attack, we conclude that the split test was properly applied to
the claimant’s injuries in this case.
                       BACKGROUND
   George Wingfield appeals from the dismissal of his claim
for workers’ compensation benefits. Wingfield filed a work-
ers’ compensation claim on January 30, 2012, alleging that he
sustained personal injuries in the form of deep vein thrombo-
sis and pulmonary embolism in an accident that occurred on
February 26, 2010. In his petition, he alleged that his injuries
arose out of the course and scope of his employment with
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Hill Brothers Transportation, Inc. (Hill Brothers), as an over-
the-road truckdriver.
    As a truckdriver, Wingfield was normally required to work
10 hours per day and would be seated during that time
period. The compensation court received evidence that pro-
longed sitting is a risk factor for the development of deep
vein thrombosis, or a blood clot forming in the deep venous
system. Wingfield had been a truckdriver for approximately
35 years. However, he had been employed by Hill Brothers
for only approximately 1 month before the February 26,
2010, accident.
    On the evening of February 25, 2010, Wingfield parked his
truck in Grand Island, Nebraska, and went to bed. He felt fine
that evening but awoke the next morning not feeling well. He
left Grand Island around 1 or 2 p.m. on February 26 and noti-
fied Hill Brothers’ dispatch that he was not feeling well and
was “headed home for days off.”
    As the day went on, Wingfield developed chest pains and
contacted his doctor. A nurse told him to come to his doc-
tor’s office as quickly as possible. Wingfield arrived at his
doctor’s office and was then hospitalized. He was diagnosed
with deep vein thrombosis in his left leg, and although it
was unconfirmed, the presence of a pulmonary embolism was
deemed likely.
    The compensation court received evidence that a pulmonary
embolism usually arises from deep vein thrombosis. When
a blood clot in the deep venous system breaks off, it may
travel through the heart and enter the pulmonary system. A
pulmonary embolism occurs when the blood clot reaches a
point within the artery of the lung where it can no longer pass
through and so becomes lodged. Depending upon the size of
the clot and whether it compromises the blood supply into the
lung, a pulmonary embolism can be fatal.
    After the February 26, 2010, accident, Wingfield had a
filter implanted to prevent future pulmonary embolisms. He
also experienced pain in his legs, swelling in his legs and feet,
blood clots behind his knees, leg sores, shortness of breath,
and difficulty standing and sitting for long periods of time.
Although he returned to his employment with Hill Brothers,
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	                     WINGFIELD v. HILL BROS. TRANSP.	177
	                            Cite as 288 Neb. 174

he needed to take more frequent breaks to walk around and
exercise. He quit working for Hill Brothers when he injured his
lower back in a fall from his truck in October 2010.
   Although Wingfield alleged that he developed deep vein
thrombosis and pulmonary embolism as a result of the February
26, 2010, accident, that episode was not Wingfield’s first diag-
nosis of those conditions. Wingfield had been hospitalized for
the same conditions on two prior occasions before starting his
employment with Hill Brothers. The first episode occurred in
September 2005. As a result of that episode, Wingfield filed
a workers’ compensation claim in Missouri, claiming that he
was “[d]riving a truck and developed deep vein thrombosis and
pulmonary embolism.” This claim is ongoing.
   Wingfield’s second episode of deep vein thrombosis and
pulmonary embolism occurred on December 31, 2009, approxi-
mately 1 month before he began his employment with Hill
Brothers. On that day, Wingfield saw his doctor and com-
plained of shooting pain in his sternal area, shortness of breath,
and pain in his legs and behind his left knee. He was hospital-
ized and diagnosed with deep vein thrombosis in his left lower
extremity and “bilateral pulmonary emboli” in his pulmonary
arteries. As a result of these prior episodes of deep vein throm-
bosis and pulmonary embolism, Wingfield was prescribed life-
time or long-term use of anticoagulation medication to prevent
the formation of future blood clots.
   The compensation court dismissed Wingfield’s claim for
benefits with respect to the February 26, 2010, accident. In
doing so, the court noted that Wingfield’s prior episodes of
deep vein thrombosis and pulmonary embolism required it
to consider the appropriate level of proof necessary to estab-
lish that his injuries arose out of his employment with Hill
Brothers. For guidance, the court looked to Leitz v. Roberts
Dairy,1 in which we indicated that causation in heart attack
cases requires proof of both legal and medical causation.
The court applied this split test of causation to Wingfield’s
claim, finding that “the distinction between the movement of
a blood clot (prompted by prolonged sitting at work) through

 1	
      Leitz v. Roberts Dairy, 237 Neb. 235, 465 N.W.2d 601 (1991).
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a vein leading to the lung (pulmonary embolism) and a clot
. . . flowing through an artery to the heart (heart attack) is less
than clear.”
    After applying the split causation test, the compensation
court concluded that Wingfield had failed to prove medical
causation—that the employment contributed in some material
and substantial degree to cause the injury.2 In support of its
conclusion, the court relied upon the opinion of Dr. Michael
Del Core, who was retained to review the medical records
in this case. Del Core concluded that Wingfield was “not
adequately anticoagulated” at the time of his admission to the
hospital on February 26, 2010. His anticoagulation medication
was at a nontherapeutic level and was consistent with a person
who was not taking any type of anticoagulation medication.
Thus, Del Core concluded that the “February 26 episode of
pulmonary emboli was not specifically work related but rather
a combination of multiple risk factors, most importantly, inad-
equate anticoagulation at the time of admission.”
    The compensation court found Del Core’s opinion to be
persuasive and, thus, concluded that Wingfield had failed to
establish that his employment with Hill Brothers caused the
February 26, 2010, accident. It therefore dismissed Wingfield’s
claim. Wingfield timely appealed, and we moved the case to
our docket pursuant to statutory authority.3

                 ASSIGNMENTS OF ERROR
   Wingfield assigns that the compensation court erred in (1)
applying the causation standard used in heart attack cases;
(2) finding that his injury did not arise out of the course and
scope of his employment with Hill Brothers; (3) sustaining
Hill Brothers’ objection to exhibits regarding medical bills
and mileage reimbursement requests; and (4) failing to cal-
culate his average weekly wage and award temporary total
disability benefits, permanent total disability benefits, past
medical bills, future medical expenses, penalties, attorney
fees, and interest.

 2	
      See id.
 3	
      See Neb. Rev. Stat. § 24-1106(3) (Reissue 2008).
                      Nebraska Advance Sheets
	                    WINGFIELD v. HILL BROS. TRANSP.	179
	                           Cite as 288 Neb. 174

                   STANDARD OF REVIEW
   [1] Pursuant to Neb. Rev. Stat. § 48-185 (Cum. Supp. 2012),
an appellate court may modify, reverse, or set aside a Workers’
Compensation Court decision only when (1) the compensa-
tion court acted without or in excess of its powers; (2) the
judgment, order, or award was procured by fraud; (3) there is
not sufficient competent evidence in the record to warrant the
making of the order, judgment, or award; or (4) the findings
of fact by the compensation court did not support the order
or award.4
   [2,3] An appellate court is obligated in workers’ compensa-
tion cases to make its own determinations as to questions of
law.5 The issue in regard to causation of an injury or disability
is one for determination by the fact finder, whose findings will
not be set aside unless clearly wrong.6

                          ANALYSIS
   We first address Wingfield’s assertion that the compensation
court erred in applying the split test of causation to his injuries
of deep vein thrombosis and pulmonary embolism. We then
turn to whether the court erred in finding that his injuries did
not arise out of the course and scope of his employment with
Hill Brothers. Because these two issues control the disposition
of Wingfield’s remaining assignments of error, they comprise
the majority of our analysis.

                            Causation
   We first note that the record clearly establishes that
Wingfield had a preexisting condition of deep vein throm-
bosis prior to his employment with Hill Brothers. We must
therefore determine the proper causation standard applicable
to his February 26, 2010, episode of deep vein thrombosis
and pulmonary embolism. The compensation court applied the
split causation test applicable to a claimant with a preexisting

 4	
      Stueve v. Valmont Indus., 277 Neb. 292, 761 N.W.2d 544 (2009).
 5	
      Id.
 6	
      Way v. Hendricks Sodding & Landscaping, Inc., 236 Neb. 519, 462
      N.W.2d 99 (1990).
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condition in a heart attack case. But Wingfield contends that
the court should have applied the causation standard applicable
to a claimant with a preexisting condition in a case not involv-
ing heart attack.
   [4-6] As noted above, in heart attack cases, the heart injury
causation issue consists of two elements: (1) legal causation
and (2) medical causation.7 When a preexisting disease or con-
dition is present, we have adopted the following test for legal
causation: An exertion- or stress-caused heart injury to which
the claimant’s preexisting heart disease or condition contributes
is compensable only if the claimant shows that the exertion
or stress encountered during employment is greater than that
experienced during the ordinary nonemployment life of the
employee or any other person.8 If it is claimed that an injury
was the result of stress or exertion in the employment, medical
causation is established by a showing by a preponderance of
the evidence that the employment contributed in some material
and substantial degree to cause the injury.9
   [7,8] But in compensation cases not involving injury from
heart attack, a claimant with a preexisting condition must
prove by a preponderance of evidence that the claimed injury
or disability was caused by the claimant’s employment and is
not merely the progression of a condition present before the
employment-related incident alleged as the cause of the dis-
ability.10 Such claimant may recover when an injury, arising
out of and in the course of employment, combines with a pre-
existing condition to produce disability, notwithstanding that in
the absence of the preexisting condition, no disability would
have resulted.11
   [9] In determining the proper causation standard appli-
cable to Wingfield’s injuries, we review the rationale for the

 7	
      See Zessin v. Shanahan Mechanical & Elec., 251 Neb. 651, 558 N.W.2d
      564 (1997).
 8	
      Id.
 9	
      Id.
10	
      See Swanson v. Park Place Automotive, 267 Neb. 133, 672 N.W.2d 405
      (2003).
11	
      Id.
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	                     WINGFIELD v. HILL BROS. TRANSP.	181
	                            Cite as 288 Neb. 174

development of the split causation test in heart attack cases for
guidance. When a workers’ compensation claimant has suffered
a heart attack, the foremost and essential problem is causation,
that is, whether the employment caused an employee’s injury
or death from a heart attack.12 This is because the generalized
nature of heart attack cases makes it difficult to attribute the
attack to the work.13 But disability or death from heart attack
is not compensable unless the injury or death arose out of the
employment.14 Thus, the question to be determined is whether
the injury was the result of a personal rather than an employ-
ment risk.15 The split test of causation helps to resolve this
question. Through the separation of legal and medical causa-
tion, it is possible to compensate those heart attack victims
whose work placed a greater strain on their hearts than would
ordinary nonemployment life.16
   Under the legal test, the claimant must establish that the
proximate cause of the heart attack was work related and
thereby break any causal connection between the natural pro-
gression of a preexisting condition or disease and the injury
at the workplace.17 Otherwise, the fact that the heart injury
occurred at work would be strictly fortuitous.18 Under the med-
ical test, “the doctors must say whether the exertion (having
been held legally sufficient to support compensation) in fact
caused this collapse.”19 The medical test establishes whether
the exertion contributed causally to the collapse as a matter of
medical fact.20

12	
      Zessin, supra note 7.
13	
      Morton v. Hunt Transp., 240 Neb. 63, 480 N.W.2d 217 (1992).
14	
      See Sellens v. Allen Products Co., Inc., 206 Neb. 506, 293 N.W.2d 415
      (1980).
15	
      Id.
16	
      Morton, supra note 13.
17	
      See Leitz, supra note 1.
18	
      Id.
19	
      2 Arthur Larson & Lex K. Larson, Larson’s Workers’ Compensation Law
      § 46.03[1] at 46-6 (2013).
20	
      Id., § 46.03[8].
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   The above review reveals that the split test of causation
developed as a result of the difficulties in distinguishing those
injuries from heart attack that arose from a personal, rather
than an employment, risk. But workers’ compensation cases
not involving heart attack do not present such difficulties
in determining causation. That is why in Engel v. Nebraska
Methodist Hospital,21 we declined to extend the exertion
“‘greater than nonemployment life’” test to the claimant’s
back injury. In that case, we emphasized the unique problem
of proving causation in heart attack cases and concluded that
there was no reason to extend the rule to other cases where the
proof of causation is not usually as complex.22 We similarly
declined to extend the split test of causation to the claim-
ant’s carpal tunnel syndrome in Morton v. Hunt Transp.23 In
Morton, we again reasoned that the claimant’s injury shared
none of the difficulties of etiology surrounding heart attacks
and reaffirmed that the split test of causation has no appli-
cation to injuries for which difficult issues of causation are
not present.24
   But we have not limited the split test of causation to inju-
ries arising from heart attack. In Smith v. Fremont Contract
Carriers,25 we recognized that the split causation test was logi-
cally applicable to stroke cases. In doing so, we acknowledged
the unique problem of proving causation of a heart attack
when a preexisting condition is present and recognized that
such a problem is also present when a claimant has suffered
a stroke.26
   We see the same problem of proving causation in Wingfield’s
injuries of deep vein thrombosis and pulmonary embolism. The
compensation court received evidence that Wingfield’s injuries

21	
      Engel v. Nebraska Methodist Hospital, 209 Neb. 878, 883, 312 N.W.2d
      281, 285 (1981).
22	
      See id.
23	
      Morton, supra note 13.
24	
      See id.
25	
      Smith v. Fremont Contract Carriers, 218 Neb. 652, 358 N.W.2d 211
      (1984).
26	
      See id.
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	                     WINGFIELD v. HILL BROS. TRANSP.	183
	                            Cite as 288 Neb. 174

could have arisen from multiple causes, both personal and
employment related. These causes included inadequate antico-
agulation, obesity, trauma, surgery, heredity, prolonged sitting,
and smoking. Thus, Wingfield’s injuries are distinguishable
from the claimants’ injuries in Engel (back injury) and Morton
(carpal tunnel syndrome) where it was clear that the injuries in
those cases were precipitated by some employment-related risk
or event.
   The possible causes for Wingfield’s development of deep
vein thrombosis and pulmonary embolism demonstrate that his
injuries were akin to the generalized nature of heart attacks,
making it difficult to factually attribute his injuries to the
work.27 As in cases of heart attack or stroke, the compensation
court was required to address complex issues of causation and
to determine whether Wingfield’s injuries arose from a per-
sonal or employment-related risk. We therefore find it logical
that the court extended the split test of causation to Wingfield’s
injuries in this case.
   In concluding that the compensation court did not err in
applying the split test of causation to Wingfield’s injuries,
we also note the similarities in origin between his injuries
and a heart attack. As the court observed, the significance
of a blood clot forming in the deep venous system and caus-
ing pulmonary embolism, rather than a blood clot forming in
an artery of the heart and causing heart attack, is less than
clear. Common knowledge informs us that both conditions
share many of the same risk factors. That a blood clot might
develop in one part of the body rather than another does not
strike us as warranting the application of two different stan-
dards of causation.
   We also reject Wingfield’s argument that the legal cause
prong of the split causation test cannot be applied to his inju-
ries. Wingfield argues that because his injuries were caused
by inactivity, there is no stress or exertion by which to
determine legal causation. But Wingfield’s argument ignores
that “stress” encompasses more than physical activity. Stress
also includes “a physical, chemical, or emotional factor . . .

27	
      See Morton, supra note 13.
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to which an individual fails to make a satisfactory adapta-
tion, and which causes physiologic tensions that may be a
contributory cause of disease.”28 We make no comment as to
whether Wingfield’s inactivity constitutes stress in this sense.
We merely note that the lack of physical activity precipitat-
ing Wingfield’s injuries does not render the legal cause prong
inapplicable to his claim. This assignment of error is with-
out merit.

                       Course and Scope
                        of Employment
   Wingfield assigns that the compensation court erred in
finding that his injuries did not arise out of the course and
scope of his employment with Hill Brothers. In support of this
assigned error, he argues that the court ignored the fact that he
passed a physical examination prior to beginning his employ-
ment with Hill Brothers, that the court erroneously made find-
ings of fact with respect to the expert testimony offered by the
parties, and that the court incorrectly relied upon the opinion
of Del Core.
   [10] We see no need to address Wingfield’s specific argu-
ments as to this assignment of error. The issue in regard to
causation of an injury or disability is one for determination
by the fact finder, whose findings will not be set aside unless
clearly wrong.29 The compensation court found that Wingfield
had failed to establish the medical cause prong of the split
causation test. Its determination was not clearly wrong. As
we have noted, to establish medical causation, Wingfield was
required to show that his employment contributed in some
material and substantial degree to cause his injuries. But
Del Core opined that the primary and most likely cause of the
February 26, 2010, accident was Wingfield’s inadequate level
of anticoagulation—a factor independent of his employment
with Hill Brothers. The court found this evidence to be per-
suasive, and it was entitled to do so. The single judge of the

28	
      Webster’s Third New International Dictionary of the English Language,
      Unabridged 2260 (1993).
29	
      Way, supra note 6.
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	                     WINGFIELD v. HILL BROS. TRANSP.	185
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Workers’ Compensation Court is the sole judge of the credibil-
ity of the witnesses and the weight to be given their testimony,
even where the issue is not one of live testimonial credibility.30
This assigned error is without merit.
                    R emaining Assignments
                           of Error
   Wingfield’s remaining assignments of error assert that the
compensation court erred in (1) sustaining Hill Brothers’
objection to exhibits regarding medical bills and mileage
reimbursement requests and (2) failing to calculate his aver-
age weekly wage and award temporary total disability ben-
efits, permanent total disability benefits, past medical bills,
future medical expenses, penalties, attorney fees, and inter-
est. Because the compensation court correctly found that
Wingfield had failed to prove that his injuries arose out of
the course and scope of his employment with Hill Brothers, it
did not err in excluding evidence as to his expenses or in fail-
ing to award the requested relief. These assignments of error
lack merit.
                         CONCLUSION
   The split test of causation developed in the context of heart
attack cases due to the difficulties in attributing the cause of a
heart attack to the claimant’s work. Because complex issues of
causation were present in Wingfield’s injuries, and the injuries
could have arisen from personal or employment-related risks,
we find no error in the application of the split causation test
to this case. And because the compensation court’s finding
as to causation was not clearly wrong, we reject Wingfield’s
remaining assignments of error. The dismissal of Wingfield’s
claim is affirmed.
                                                       Affirmed.

30	
      See Swanson, supra note 10.
