[Biventricular-pulmonary interaction as the prime mechanism in the adaptation of the human heart to orthostatic posture].
The purpose was to identify the basic circulatory adjustments to the erect position in man and what the role may be of the heart-lung coupling. Requirements for this study are that: subjects be normal, changes in posture be gradual; pulmonary venous flow, ventricular filling and output be assessed; the methods be noninvasive. In 10 normal men (mean age 34 +/- 8 years) the flow pattern in the right upper pulmonary vein and through the atrioventricular mitral valve, and the right and left ventricular (RV and LV) end-diastolic dimensions were assessed with Doppler echocardiography, in the supine position, after 20, 40 and 60 degrees tilting for 10 min. At 20 degrees displacement: blood pressure, heart rate, stroke volume and LV dimension did not change: RV dimension reduced: pulmonary venous forward flow velocity diminished during systole (X wave) and rose in diastole (Y wave); E wave velocity of the mitral flow and the E/A ratio reduced (consistent with a lower atrioventricular pressure gradient); difference between duration of the pulmonary venous flow reversal during atrial contraction (Z wave) and duration of the mitral A wave (the difference is an index of LV end-diastolic pressure) also diminished, suggesting an improvement of LV compliance. Tilting at 40 and 60 degrees were associated with increase in heart rate and diastolic blood pressure; decrease in systolic blood pressure and stroke volume; reduction of diastolic dimension of both ventricles; some enhancement of the flow changes already described. X was related to stroke volume while supine (r = 0.75; p < 0.01) and not during tilting; at any level of tilting, X/Y ratio was inversely related to the E/A ratio and directly related to the difference in duration between Z and A. During vertical displacement, blood shifts from lungs to systemic circulation resulting in: contribution to replenishment of the arterial side of the circuit; enhancement in LV compliance, due to reduction of RV diastolic volume (interdependence) and pericardial constraint; facilitation and predominance of blood drainage for the lungs during ventricular diastole. Thus, the basic adaptation to erect positioning in man seems to be a mechanical one, mainly consisting of an interplay between heart and lungs. Increase in heart rate and vasoconstriction appear to be supportive mechanisms at more vertical postures.
Guazzi
M
M
Istituto di Cardiologia, Università degli Studi, Milano.
Maltagliati
A
A
Tamborini
G
G
D000222:Adaptation, Physiological; D000328:Adult; D000704:Analysis of Variance; D004452:Echocardiography / Q000706:statistics & numerical data; D006321:Heart / Q000502:physiology*; D006352:Heart Ventricles / Q000000981:diagnostic imaging; D006801:Humans; D016014:Linear Models; D008168:Lung / Q000000981:diagnostic imaging / Q000502:physiology*; D008297:Male; D011187:Posture / Q000502:physiology*; D011652:Pulmonary Circulation / Q000502:physiology; D012016:Reference Values; D018667:Tilt-Table Test / Q000706:statistics & numerical data; D013997:Time Factors; D016276:Ventricular Function