HANDBOOK OF PHYSIOLOGY 



CIRCULATION II 



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 60 





fig. 40. Effects of a prolonged forced expiration on systemic arterial pressures {upper tracing) and 

 right ventricular {lower /racing) pressures in a patient with chronic pulmonary emphysema and 

 fibrosis. Ten seconds after the start of expiration (solid arrow), the amplitude of the RV pressure 

 pulse begins to increase, after several beats, there is a progressive rise in the femoral arterial systolic, 

 diastolic, and pulse pressures. This suggests that as the flow of blood into the thorax is impeded, the 

 volume of the peripheral venous reservoir slowly increases until the venous pressure becomes suffi- 

 ciently great again to increase the right heart filling and output, in spite of the continued elevation 

 of the intrathoracic pressure. During the succeeding inspiration (hollow arrow), a further augmenta- 

 tion of the right ventricular pulse pressure occurs (last four beats). [After Lauson, el at. (253).] 



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OES 



fig. 41. Effect of the Valsalva maneuver on brachial arterial pressure (BA) and "transmural" 

 pulmonary arterial pressure (dPA). The changes in intrathoracic pressure, measured as the esopha- 

 geal pressure (OES), indicate the onset, duration, and end of the expiratory effort. All pressures are 

 in mm Hg. The overshoot in the systemic arterial response following the Valsalva maneuver is 

 ascribed to reflex vasoconstriction. On the other hand, the pattern of change in pulmonary arterial 

 pressure is attributed to mechanical events, i.e., to alterations in venous return and right ventricular 

 output. [After Lee et at. (255).] 



At the start of negative (intrapulmonary) pressure 

 breathing the systemic venous return to the lungs 

 and the pulmonary blood volume increase (49). In 

 contrast to positive pressure breathing, the negative 

 intrapulmonary pressures distend the intrapulmonary 

 vessels (256). At the small lung volumes, associated 

 with continuous negative pressure breathing, atelec- 

 tasis may develop. 



Cough 



During a cough, pressure referred to atmosphere 

 rises simultaneously and equally in the thorax 

 (fig. 21), abdomen, and cerebrospinal canal (190). 

 The increase in pressure (which may transiently reach 



levels of 1 50 mm Hg) does not strain the intrathoracic 

 (255) or abdominal or cerebrospinal vessels, and does 

 not, per se, affect the pressure gradient which drives 

 blood along the pulmonary vascular tree. However, 

 it is propagated to the peripheral arterial tree where 

 it causes a marked increase in the transmural distend- 

 ing pressure (190). 



Prolonged Expiration 



During a prolonged expiration (fig. 40), the ampli- 

 tude of the pulmonary arterial (and right ventricular) 

 pressure pulse first decreases and then gradually in- 

 creases; the systemic arterial blood pressures undergo 

 a similar pattern of change. This sequence has been 



