Cardiovascular changes in conscious dogs during spontaneous deep breaths

Abstract

Cardiovascular functions were evaluated beat by beat during 29 spontaneous deep breaths in three conscious dogs. When pleural pressure was significantly lower than during quiet breathing, stroke volume was reduced, heart rate elevated, as well as transmural pressure in the pulmonary artery (PPA-Ppl) and in the thoracic aorta (PAO-Ppl); the left ventricular filling pressure (LVEDP-Ppl) did not decrease. The authors suggest that these findings are not consistent with the classical hypothesis which explains the decrease in left ventricular output primarily by a reduction in the venous return to the left heart. The results indicate that the decrease in pleural pressure is responsible for an increase in the afterload on the left heart and suggest that this is the predominate factor in the reduction of the stroke volume without decrease in left ventricular filling pressure.

Slow and fast changes in transmural pulmonary artery pressure in obstructive sleep apnoea

“…However, other studies have demonstrated that negative intrathoracic pressure increases transmural Ppa [18][19][20]. Such an increase could be consequent to an increase in right ventricular preload [21] and output [21,22], or to an increase in left ventricular afterload [18][19][20]23].…”

“…Such an increase could be consequent to an increase in right ventricular preload [21] and output [21,22], or to an increase in left ventricular afterload [18][19][20]23]. However, PODSZUS and co-workers [6] considered negative intrathoracic pressure as a possible cause for a decrease, and not for an increase, in Ppa, due to possible extrathoracic vein collapse and venous return limitation; in fact, venous return was found to be limited by extrathoracic vein collapse when threshold negative intrathoracic pressure levels were exceeded [24].…”

Terrestrial locomotion does not constrain venous return in the American alligator,Alligator mississippiensis

“…Collapse of the inferior vena cava during inspiration decreases venous return from the lower extremities and is associated with a decrease in splanchnic blood flow (Abel and Waldhausen, 1969;Rabinovici and Navot, 1980;Willeput et al, 1984). Left ventricular stroke volume can also be reduced during inspiration in mammals (Charlier et al, 1974;Hoffman et al, 1965;Ruskin et al, 1973;Schrijen et al, 1975) due to a fall in effective ejection pressure of the left ventricle (Olsen et al, 1985). Contraction of the abdominal muscles during expiration aids venous return in mammals (Abel and Waldhausen, 1969;Youmans et al, 1963).…”

Ventricular performance related to transmural filling pressure in clinical cardiac tamponade.

“…Although the transmission of negative intrathoracic pressure to the aorta may cause a decrease in arterial pressure measured with reference to atmospheric pressure, an inspiratory decrease in arterial pulse pressure implies a decrease in left ventricular stroke volume.42 This has been attributed to a decrease in left ventricular preload43'" or an increase in afterload. 45 The inspiratory decrease in PWP -IPP reported here strongly supports preload reduction as an important mechanism of pulsus paradoxus in cardiac tamponade. If left heart filling decreases while right heart output is maintained, pooling in the pulmonary circuit necessarily occurs but attributing this effect chiefly to lung mechanics or right-left competition is difficult.…”

“…45 The curve relating transmural diastolic pressure to ventricular diastolic volume may be relatively flat in the vicinity of zero pressure, with a nearly exponential rise in pressure above this range and negative pressures at the volumes below the equilibrium range. 31 35 Careful measurements have shown nearly exact equality of left ventricular, right ventricular, and intrapericardial pressures throughout diastole in certain cases of tamponade, confirming that a range of ventricular volumes from early to late diastole may occur at nearly zero transmural diastolic pressure.…”