Distribution of lung density after strenuous, prolonged exercise

The Effect of an Olympic Distance Triathlon on Pulmonary Diffusing Capacity and its Recovery 24 Hours Later

The Olympic distance triathlon includes maximal exercise bouts with transitions between the activities. This study investigated the effect of an Olympic distance triathlon (1.5-km swim, 40-km bike, 10-km run) on pulmonary diffusion capacity (DLCO). In nine male triathletes (age: 24 ± 4.7 years), we measured DLCO and calculated the DLCO to alveolar volume ratio (DLCO/VA) and performed spirometry testing before a triathlon (pre-T), 2 hours after the race (post-T), and the day following the race (post-T-24 h). DLCO was measured using the 9-s breath-holding method. We found that (1) DLCO decreased significantly between pre- and post-T values (38.52 ± 5.44 vs. 35.92 ± 6.63 ml∙min^-1∙mmHg^-1) (p < 0.01) and returned to baseline at post-T-24 h (38.52 ± 5.44 vs. 37.24 ± 6.76 ml∙min^-1∙mmHg^-1, p > 0.05); (2) DLCO/VA was similar at the pre-, post- and post-T-24 h DLCO comparisons; and (3) forced expiratory volume in the first second (FEV₁) and mean forced expiratory flow during the middle half of vital capacity (FEF25-75%) significantly decreased between pre- and post-T and between pre- and post-T-24-h (p < 0.02). In conclusion, a significant reduction in DLCO and DLCO/VA 2 hours after the triathlon suggests the presence of pulmonary interstitial oedema. Both values returned to baseline 24 hours after the race, which reflects possible mild and transient pulmonary oedema with minimal physiological significance.

Swimming induced pulmonary oedema in athletes - a systematic review and best evidence synthesis

Background

Swimming induced pulmonary oedema is an uncommon occurrence and usually presents during strenuous distance swimming in cold water. The prevalence is most likely underreported and the underlying mechanisms are controversial. The purpose of this study was to summarize the evidence with regards to prevalence, pathophysiology and treatment of swimming induced pulmonary oedema in endurance athletes.

Methods

Medline, Embase, Scopus and Google Scholar were searched and level I-IV from 1970 to 2017 were included. For clinical studies, only publications reporting on swimming-induced pulmonary oedema were considered. Risk of bias was assessed with the ROBINS-I tool, and the quality of evidence was assessed with the Cochrane GRADE system. For data synthesis and analysis, a best evidence synthesis was used.

Results

A total of 29 studies were included (174 athletes). The most common symptom was cough, dyspnoea, froth and haemoptysis. The risk of bias for the clinical studies included 13 with moderate risk, 3 with serious, and 4 with critical. Four of the pathophysiology studies had a moderate risk, 3 a serious risk, and 1 a critical risk of bias. A best evidence analysis demonstrated a strong association between cold water immersion and in increases of CVP (central venous pressure), MPAP (mean pulmonary arterial pressure), PVR (peripheral vascular resistance) and PAWP (pulmonary arterial wedge pressure) resulting in interstitial asymptomatic oedema.

Conclusion

The results of this study suggest a moderate association between water temperature and the prevalence of SIPE. The presence of the clinical symptoms cough, dyspnoea, froth and haemoptysis are strongly suggestive of SIPE during or immediately following swimming. There is only limited evidence to suggest that there are pre-existing risk factors leading to SIPE with exposure to strenuous physical activity during swimming. There is strong evidence that sudden deaths of triathletes are often associated with cardiac abnormalities.

No compensatory lung growth after resection in a one-year follow-up cohort of patients with lung cancer

Background

As compensatory lung growth after lung resection has been studied in animals of various ages and in one case report in a young adult, it has not been studied in a cohort of adults operated for lung cancer.

Methods

A prospective study including patients with lung cancer was conducted over two years. Parenchymal mass was calculated using computed tomography before (M0) and at 3 and 12 months (M3 and M12) after surgery. Respiratory function was estimated by plethysmography and CO/NO lung transfer (D_LCO and D_LNO). Pulmonary capillary blood volume (Vc) and membrane conductance for CO (Dm_CO) were calculated. Insulin-like growth factor-1 (IGF-1) and insulin-like growth factor binding protein-3 (IGFBP-3) plasma concentrations were measured simultaneously.

Results

Forty-nine patients underwent a pneumonectomy (N=12) or a lobectomy (N=37) thirty two completed the protocol. Among all patients, from M3 to M12 the masses of the operated lungs (239±58 to 238±72 g in the lobectomy group) and of the non-operated lungs (393±84 to 377±68 g) did not change. Adjusted by the alveolar volume (V_A), D_LNO/V_A decreased transiently by 7% at M3, returning towards the M0 value at M12. Both Vc and Dm_CO increased slightly between M3 and M12. IGF-1 and IGFBP-3 concentrations did not change at M3, IGF-1 decreased significantly from M3 to M12.

Conclusions

Compensatory lung growth did not occur over one year after lung surgery. The lung function data could suggest a slight recruitment or distension of capillaries owing to the likely hemodynamic alterations. An angiogenesis process is unlikely.

Maximal exercise does not increase ventilation heterogeneity in healthy trained adults

The effect of exercise on ventilation heterogeneity has not been investigated. We hypothesized that a maximal exercise bout would increase ventilation heterogeneity. We also hypothesized that increased ventilation heterogeneity would be associated with exercise‐induced arterial hypoxemia (EIAH). Healthy trained adult males were prospectively assessed for ventilation heterogeneity using lung clearance index (LCI), S_cond, and S_acin at baseline, postexercise and at recovery, using the multiple breath nitrogen washout technique. The maximal exercise bout consisted of a maximal, incremental cardiopulmonary exercise test at 25 watt increments. Eighteen subjects were recruited with mean ± SD age of 35 ± 9 years. There were no significant changes in LCI, S_cond, or S_acin following exercise or at recovery. While there was an overall reduction in SpO₂ with exercise (99.3 ± 1 to 93.7 ± 3%, P < 0.0001), the reduction in SpO₂ was not associated with changes in LCI, S_cond or S_acin. Ventilation heterogeneity is not increased following a maximal exercise bout in healthy trained adults. Furthermore, EIAH is not associated with changes in ventilation heterogeneity in healthy trained adults.

Exercise-induced interstitial pulmonary edema at sea-level in young and old healthy humans

We asked whether aged adults are more susceptible to exercise-induced pulmonary edema relative to younger individuals. Lung diffusing capacity for carbon monoxide (DLCO), alveolar-capillary membrane conductance (Dm) and pulmonary-capillary blood volume (Vc) were measured before and after exhaustive discontinuous incremental exercise in 10 young (YNG; 27±3 years) and 10 old (OLD; 69±5 years) males. In YNG subjects, Dm increased (11±7%, P=0.031), Vc decreased (-10±9%, P=0.01) and DLCO was unchanged (30.5±4.1 vs. 29.7±2.9mL/min/mmHg, P=0.44) pre- to post-exercise. In OLD subjects, DLCO and Dm increased (11±14%, P=0.042; 16±14%, P=0.025) but Vc was unchanged (58±23 vs. 56±23mL, P=0.570) pre- to post-exercise. Group-mean Dm/Vc was greater after vs. before exercise in the YNG and OLD subjects. However, Dm/Vc was lower post-exercise in 2 of the 10 YNG (-7±4%) and 2 of the 10 OLD subjects (-10±5%). These data suggest that exercise decreases interstitial lung fluid in most YNG and OLD subjects, with a small number exhibiting evidence for exercise-induced pulmonary edema.

Genetic variation of αENaC influences lung diffusion during exercise in humans

Exercise, decompensated heart failure, and exposure to high altitude have been shown to cause symptoms of pulmonary edema in some, but not all, subjects, suggesting a genetic component to this response. Epithelial Na(+) Channels (ENaC) regulate Na(+) and fluid reabsorption in the alveolar airspace in the lung. An increase in number and/or activity of ENaC has been shown to increase lung fluid clearance. Previous work has demonstrated common functional genetic variants of the α-subunit of ENaC, including an A→T substitution at amino acid 663 (αA663T). We sought to determine the influence of the T663 variant of αENaC on lung diffusion at rest and at peak exercise in healthy humans. Thirty healthy subjects were recruited for study and grouped according to their SCNN1A genotype [n=17 vs. 13, age=25±7 years vs. 30±10 years, BMI=23±4 kg/m(2) vs. 25±4 kg/m(2), V(O2 peak) = 95±30%pred. vs. 100±31%pred., mean±SD, for AA (homozygous for αA663) vs. AT/TT groups (at least one αT663), respectively]. Measures of the diffusing capacity of the lungs for carbon monoxide (DL(CO)), the diffusing capacity of the lungs for nitric oxide (DL(NO)), alveolar volume (V(A)), and alveolar-capillary membrane conductance (D(M)) were taken at rest and at peak exercise. Subjects expressing the AA polymorphism of ENaC showed a significantly greater percent increase in DL(CO) and DL(NO), and a significantly greater decrease in systemic vascular resistance from rest to peak exercise than those with the AT/TT variant (DL(CO)=51±12% vs. 36±17%, DL(NO)=51±24% vs. 32±25%, SVR=-67±3 vs. -50±8%, p<0.05). The AA ENaC group also tended to have a greater percent increase in DL(CO)/VA from rest to peak exercise, although this did not reach statistical significance (49±26% vs. 33±26%, p=0.08). These results demonstrate that genetic variation of the α-subunit of ENaC at amino acid 663 influences lung diffusion at peak exercise in healthy humans, suggesting differences in alveolar Na(+) and, therefore, fluid handling. These findings could be important in determining who may be susceptible to pulmonary edema in response to various clinical or environmental conditions.

Early subclinical increase in pulmonary water content in athletes performing sustained heavy exercise at sea level: ultrasound lung comet-tail evidence

Whether prolonged strenuous exercise performed by athletes at sea level can produce interstitial pulmonary edema is under debate. Chest sonography allows to estimate extravascular lung water, creating ultrasound lung comet-tail (ULC) artifacts. The aim of the study was to determine whether pulmonary water content increases in Ironmen (n = 31) during race at sea level and its correlation with cardiopulmonary function and systemic proinflammatory and cardiac biohumoral markers. A multiple factor analysis approach was used to determine the relations between systemic modifications and ULCs by assessing correlations among variables and groups of variables showing significant pre-post changes. All athletes were asymptomatic for cough and dyspnea at rest and after the race. Immediately after the race, a score of more than five comet tail artifacts, the threshold for a significant detection, was present in 23 athletes (74%; 16.3 ± 11.2; P < 0.01 ULC after the race vs. rest) but decreased 12 h after the end of the race (13 athletes; 42%; 6.3 ± 8.0; P < 0.01 vs. soon after the race). Multiple factor analysis showed significant correlations between ULCs and cardiac-related variables and NH(2)-terminal pro-brain natriuretic peptide. Healthy athletes developed subclinical increase in pulmonary water content immediately after an Ironman race at sea level, as shown by the increased number of ULCs related to cardiac changes occurring during exercise. Hemodynamic changes are one of several potential factors contributing to the mechanisms of ULCs.

Lung density is not altered following intense normobaric hypoxic interval training in competitive female cyclists

Noninvasive imaging techniques have been used to assess pulmonary edema following exercise but results remain equivocal. Most studies examining this phenomenon have used male subjects while the female response has received little attention. Some suggest that women, by virtue of their smaller lungs, airways, and diffusion surface areas may be more susceptible to pulmonary limitations during exercise. Accordingly, the purpose of this study was to determine if intense normobaric hypoxic exercise could induce pulmonary edema in women. Baseline lung density was obtained in eight highly trained female cyclists (mean +/- SD: age = 26 +/- 7 yr; height = 172.2 +/- 6.7 cm; mass = 64.1 +/- 6.7 kg; Vo(2max) = 52.2 +/- 2.2 ml.kg(-1).min(-1)) using computed tomography (CT). CT scans were obtained at the level of the aortic arch, the tracheal carina, and the superior end plate of the tenth thoracic vertebra. While breathing 15% O(2), subjects then performed five 2.5-km cycling intervals [mean power = 212 +/- 31 W; heart rate (HR) = 94.5 +/- 2.2%HRmax] separated by 5 min of recovery. Throughout the intervals, subjects desaturated to 82 +/- 4%, which was 13 +/- 2% below resting hypoxic levels. Scans were repeated 44 +/- 8 min following exercise. Mean lung density did not change from pre (0.138 +/- 0.014 g/ml)- to postexercise (0.137 +/- 0.011 g/ml). These findings suggest that pulmonary edema does not occur in highly trained females following intense normobaric hypoxic exercise.

Human lung density is not altered following normoxic and hypoxic moderate-intensity exercise: implications for transient edema

The purpose of this study was to examine the effects of exercise on extravascular lung water as it may relate to pulmonary gas exchange. Ten male humans underwent measures of maximal oxygen uptake (Vo2 max) in two conditions: normoxia (N) and normobaric hypoxia of 15% O2 (H). Lung density was measured by quantified MRI before and 48.0 +/- 7.4 and 100.7 +/- 15.1 min following 60 min of cycling exercise in N (intensity = 61.6 +/- 9.5% Vo2 max) and 55.5 +/- 9.8 and 104.3 +/- 9.1 min following 60 min cycling exercise in H (intensity = 65.4 +/- 7.1% hypoxic Vo2 max), where Vo2 max = 65.0 +/- 7.5 ml x kg(-1) x min(-1) (N) and 54.1 +/- 7.0 ml x kg(-1) x min(-1) (H). Two subjects demonstrated mild exercise-induced arterial hypoxemia (EIAH) [minimum arterial oxygen saturation (SaO2 min) = 94.5% and 93.8%], and seven subjects demonstrated moderate EIAH (SaO2 min = 91.4 +/- 1.1%) as measured noninvasively during the Vo2 max test in N. Mean lung densities, measured once preexercise and twice postexercise, were 0.177 +/- 0.019, 0.181 +/- 0.019, and 0.173 +/- 0.019 g/ml (N) and 0.178 +/- 0.021, 0.174 +/- 0.022, and 0.176 +/- 0.019 g/ml (H), respectively. No significant differences (P > 0.05) were found in lung density following exercise in either condition or between conditions. Transient interstitial pulmonary edema did not occur following sustained steady-state cycling exercise in N or H, indicating that transient edema does not result from pulmonary capillary leakage during sustained submaximal exercise.

Evidence of pulmonary oedema triggered by exercise in healthy humans and detected with various imaging techniques

This review summarizes current literature on pulmonary oedema triggered by above-ground exercise in healthy humans from studies that use various imaging techniques to detect oedema. Eleven studies were identified, comprising of 137 subjects (mean age = 28 years). Eighty per cent (n = 110) were males, and 20% (n = 27) were female. The studies were grouped into three different categories according to the severity of the exercise protocol, which were either prolonged, submaximal exercise of 15-min to 2 h in duration at approx. 50-75%VO(2max) and not to exhaustion (PROLONGED, n = 44), a VO(2max) test lasting 16-20 min in which the intensity of exercise was only maximum for about 2 min at the end of the test (GXT, n = 15), and maximum or near maximum effort exercise protocols at or near volitional exhaustion where the goal was to finish in the fastest possible time or maintain the highest possible workload (MAX EFFORT, n = 78). Only 16% of the subjects showed signs of oedema from PROLONGED exercise and no subjects (0%) showed signs of oedema from GXT exercise. Surprisingly, approx. 65% of the subjects showed signs of oedema triggered by MAX EFFORT exercise (chi(2) test of association; P < or = 0.01), which was independent of both sex, the level of hypoxia (inspired PO(2) = 106-118 mmHg vs. 149 mmHg), the timing of the post-exercise imaging (<10, >30 but <60 min, or >60 min) and VO(2max) (approx. 3.0 vs. approx. 4.8 L min(-1)). The data suggests that the chances of triggering pulmonary oedema from exhaustive MAX EFFORT exercise is 4x more compared with PROLONGED exercise. As well, the likelihood of triggering pulmonary oedema may be independent of lung size, sex, moderate levels of hypoxia, and aerobic fitness.

Intense hypoxic cycle exercise does not alter lung density in competitive male cyclists

We tested the hypothesis that intense short duration hypoxic exercise would result in an increase in extravascular lung water (EVLW), as evidenced by an increase in lung density. Using computed tomography (CT), baseline lung density was obtained in eight highly trained male cyclists (mean +/- SD: age = 28 +/- 8 years; height = 180 +/- 9 cm; mass = 71.6 +/- 8.2 kg; VO2max= 65.0 +/- 5.2 ml kg min(-1)). Subjects then completed an intense hypoxic exercise challenge on a cycle ergometer and metabolic data, HR and %S(p)O2 were recorded throughout. While breathing 15% O2, subjects performed five 3 km cycling intervals (mean power, 286 +/- 20 W; HR = 91 +/- 4% HRmax) separated by 5 min of recovery. From a resting hypoxic S(p)O2 of 92 +/- 4%, subjects further desaturated during exercise to 76 +/- 3%. CT scans were repeated 76 +/- 10 min (range 63-88 min) following the completion of exercise. There was no change in lung density from pre (0.18 +/- 0.02 g ml(-1)) to post-exercise (0.18 +/- 0.04 g ml(-1)). The substantial reduction in S(p)O2 may be explained by a number of potential mechanisms, including decreased pulmonary diffusion capacity, alveolar hypoventilation, reduced red cell transit time, ventilation/perfusion inequality or a temperature and pH induced rightward-shift in the oxyhaemoglobin dissociation curve. Alternatively, the integrity of the blood gas barrier may have been disrupted without any measurable increase in lung density.

Short-term hypoxic exposure at rest and during exercise reduces lung water in healthy humans

Hypoxia and hypoxic exercise increase pulmonary arterial pressure, cause pulmonary capillary recruitment, and may influence the ability of the lungs to regulate fluid. To examine the influence of hypoxia, alone and combined with exercise, on lung fluid balance, we studied 25 healthy subjects after 17-h exposure to 12.5% inspired oxygen (barometric pressure = 732 mmHg) and sequentially after exercise to exhaustion on a cycle ergometer with 12.5% inspired oxygen. We also studied subjects after a rapid saline infusion (30 ml/kg over 15 min) to demonstrate the sensitivity of our techniques to detect changes in lung water. Pulmonary capillary blood volume (Vc) and alveolar-capillary conductance (D(M)) were determined by measuring the diffusing capacity of the lungs for carbon monoxide and nitric oxide. Lung tissue volume and density were assessed using computed tomography. Lung water was estimated by subtracting measures of Vc from computed tomography lung tissue volume. Pulmonary function [forced vital capacity (FVC), forced expiratory volume after 1 s (FEV(1)), and forced expiratory flow at 50% of vital capacity (FEF(50))] was also assessed. Saline infusion caused an increase in Vc (42%), tissue volume (9%), and lung water (11%), and a decrease in D(M) (11%) and pulmonary function (FVC = -12 +/- 9%, FEV(1) = -17 +/- 10%, FEF(50) = -20 +/- 13%). Hypoxia and hypoxic exercise resulted in increases in Vc (43 +/- 19 and 51 +/- 16%), D(M) (7 +/- 4 and 19 +/- 6%), and pulmonary function (FVC = 9 +/- 6 and 4 +/- 3%, FEV(1) = 5 +/- 2 and 4 +/- 3%, FEF(50) = 4 +/- 2 and 12 +/- 5%) and decreases in lung density and lung water (-84 +/- 24 and -103 +/- 20 ml vs. baseline). These data suggest that 17 h of hypoxic exposure at rest or with exercise resulted in a decrease in lung water in healthy humans.

Radiographic evidence of pulmonary edema during high-intensity interval training in women

The purpose was to determine if an intense interval training session could produce transient pulmonary edema in women. Fourteen females [(27+/-4 years; body mass index of 21.6+/-1.5 kg/m(2)); maximal oxygen consumption = 3.12+/-0.42 L/min] performed three sets of 5 min sea-level cycling exercise with 10-min recovery between each set. Average oxygen consumption at minute 5 of each set was 96+/-5% of maximum and arterial plasma lactate concentration at minute 5 of each set was 16.0+/-3.3 mmol/L. Chest radiographs were obtained before and 33.2+/-6.1 min after exercise. Four different chest radiologists independently reviewed the radiographs for edema, and scored seven validated radiographic characteristics on a three-point scale (0-2). The overall edema score increased from 1.3+/-1.6 before exercise to 1.9+/-2.0 after exercise [P<0.05; Delta = +0.7+/-1.8, 95% CI, 0.2 to +1.1]. This study shows that an intense interval training session can cause mild, detectable pulmonary edema in some women.

Pulmonary Oedema following Exercise in Humans

Pulmonary physiologists have documented many transient changes in the lung and the respiratory system during and following exercise, including the incomplete oxygen saturation of arterial blood in some subjects, possibly due to transient pulmonary oedema. The large increase in pulmonary arterial pressure during exercise, leading to either increased pulmonary capillary leakage and/or pulmonary capillary stress failure, is likely to be responsible for any increase in extravascular lung water during exercise. The purpose of this article is to summarise the studies to date that have specifically examined lung water following exercise. A limited number of studies have been completed with the specific purpose of identifying pulmonary oedema following exercise or a similar intervention. Of these, approximately 50% have observed a positive change and the remaining have provided results that are either inconclusive or show no change in extravascular lung water. While it is difficult to draw a firm conclusion from these studies, we believe that pulmonary oedema does occur in some humans following exercise. As such, this is a phenomenon of significance to pulmonary and exercise physiologists. This possibility warrants further study in the area with more precise measurement tools than has previously been undertaken.

The lung at maximal exercise: insights from comparative physiology

Horses are bred selectively for aerobic performance and have extraordinarily high maximal oxygen consumption, approximately double the mass-specific value for human athletes. Pulmonary limitations to exercise performance are well described in these animals, including exercise-induced arterial hypoxemia and exercise-induced pulmonary hemorrhage. In human athletes, pulmonary limitations are recognized increasingly as affecting athletic performance. Potential pulmonary limitations during maximal exercise are compared in human and equine athletes.

Échanges gazeux pulmonaires pendant l’exercice musculaire chez le sujet sain

INTRODUCTION

The modifications of gas exchange on exercise reflect the consequences of the control and limits of adaptation of the respiratory apparatus to the mechanical loads imposed on the muscles and the oxygen requirements of the organism. In the majority of cases, even if the thoraco-pulmonary apparatus is perfectly adapted to the increase in these requirements, the balance between the metabolic demands of the tissues and the pulmonary supply appears difficult to satisfy beyond certain limits without hypoxaemia, particularly in those subjects with a low ventilatory response to exercise. Based on the populations reported in the literature the functional limits of the control of the thoraco-pulmonary system and the possible modifications of the structures of the lung are discussed for each of these mechanisms.

STATE OF KNOWLEDGE

At certain levels of duration and intensity of exercise there is an increase in the alveolar-arterial oxygen gradient [P(A-a)O2] associated inconsistently with a fall in PaO2. It is mainly the use of inert gas techniques that has established over many years the respective roles of the different possible patho-physiological mechanisms: shunt, unequal distribution of VA/Q ratios, limitation of alveolar-capillary diffusion and its components. The inequalities of VA/Q increase at low levels of exercise but beyond certain levels of VO2 limitation of oxygen diffusion may develop. In effect, particularly in subjects capable of high levels of exercise, the interaction between diminished transit time of the red cells in the pulmonary capillaries and possible delay in equilibration of partial pressures between the blood and gas phases may create a limitation of diffusion. This added to the inequalities of distribution of VA/Q and reduction in PVO2 leads, in certain subjects, to a transitory exercise induced hypoxaemia.

VIEWPOINTS AND CONCLUSIONS

New techniques of investigation seem to be necessary to clarify the sources of the observed changes and the development of modifications of pulmonary structure that establish the functional limits of the lungs on exercise. It remains to demonstrate the true impact of these anomalies on the limitation of human performance.

Effect of body position on measurements of diffusion capacity after exercise

BACKGROUND

Pulmonary diffusing capacity for carbon monoxide (D1co), alveolar capillary membrane diffusing capacity (Dm), and pulmonary capillary blood volume (Vc) are all significantly reduced after exercise.

OBJECTIVE

To investigate whether measurement position affects this impaired gas transfer.

METHODS

Before and one, two, and four hours after incremental cycle ergometer exercise to fatigue, single breath D1co, Dm, and Vc measurements were obtained in 10 healthy men in a randomly assigned supine and upright seated position.

RESULTS

After exercise, D1co, Dm, and Vc were significantly depressed compared with baseline in both positions. The supine position produced significantly higher values over time for D1co (5.22 (0.13) v. 4.66 (0.15) ml/min/mm Hg/l, p = 0.022) and Dm (6.78 (0.19) v. 6.03 (0.19) ml/min/mm Hg/l, p = 0.016), but there was no significant position effect for Vc. There was a similar pattern of change over time for D1co, Dm, and Vc in the two positions.

CONCLUSIONS

The change in D1co after exercise appears to be primarily due to a decrease in Vc. Although the mechanism for the reduction in Vc cannot be determined from these data, passive relocation of blood to the periphery as the result of gravity can be discounted, suggesting that active vasoconstriction of the pulmonary vasculature and/or peripheral vasodilatation is occurring after exercise.