Attenuating intrathoracic pressure swings decreases cardiac output at different intensities of exercise
Bibliographic record
Abstract
Abstract Intrathoracic pressure (ITP) swings that permit spontaneous ventilation have physiological implications for the heart. We sought to determine the effect of respiration on cardiac output () during semi‐supine cycle exercise using a proportional assist ventilator to minimize ITP changes and lower the work of breathing ( W b ). Twenty‐four participants (12 females) completed three exercise trials at 30%, 60% and 80% peak power ( W max ) with unloaded (using a proportional assist ventilator, PAV) and spontaneous breathing. Intrathoracic and intraabdominal pressures were measured with balloon catheters placed in the oesophagus and stomach. Left ventricular (LV) volumes and were determined via echocardiography. Heart rate (HR) was measured with electrocardiogram and a customized metabolic cart measured oxygen uptake (). Oesophageal pressure swings decreased from spontaneous to PAV breathing by −2.8 ± 3.1, −4.9 ± 5.7 and −8.1 ± 7.7 cmH 2 O at 30%, 60% and 80% W max , respectively ( P = 0.01). However, the decreases in W b were similar across exercise intensities (27 ± 42 vs . 35 ± 24 vs . 41 ± 22%, respectively, P = 0.156). During PAV breathing compared to spontaneous breathing, decreased by −1.0 ± 1.3 vs . −1.4 ± 1.4 vs . −1.5 ± 1.9 l min −1 (all P < 0.05) and stroke volume decreased during PAV breathing by −11 ± 12 vs . −9 ± 10 vs . −7 ± 11 ml from spontaneous breathing at 30%, 60% and 80% W max , respectively (all P < 0.05). HR was lower during PAV breathing by −5 ± 4 beats min −1 at 80% W max ( P < 0.0001). Oxygen uptake decreased by 100 ml min −1 during PAV breathing compared to spontaneous breathing at 80% W max ( P < 0.0001). Overall, attenuating ITPs mitigated LV preload and ejection, thereby suggesting that the ITPs associated with spontaneous respiration impact cardiac function during exercise. image Key points Pulmonary ventilation is accomplished by alterations in intrathoracic pressure (ITP), which have physiological implications on the heart and dynamically influence the loading parameters of the heart. Proportional assist ventilation was used to attenuate ITP changes and decrease the work of breathing during exercise to examine its effects on left ventricular (LV) function. Proportional assist ventilation with progressive exercise intensities (30%, 60% and 80% W max ) led to reductions in cardiac output at all intensities, primarily through reductions in stroke volume. Decreases in LV end‐diastolic volume (30% and 60% W max ) and increases in LV end‐systolic volume (80% W max ) were responsible for the reduction in stroke volume. The relationship between cardiac output and oxygen uptake is disrupted during respiratory muscle unloading.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one teacher head, not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".