These tools will no longer be maintained as of December 31, 2024. Archived website can be found here. PubMed4Hh GitHub repository can be found here. Contact NLM Customer Service if you have questions.


Pubmed for Handhelds

PUBMED FOR HANDHELDS

Search MEDLINE/PubMed

  • Title: [Biventricular-pulmonary interaction as the prime mechanism in the adaptation of the human heart to orthostatic posture].
    Author: Guazzi M, Maltagliati A, Tamborini G.
    Journal: Cardiologia; 1997 Jan; 42(1):69-76. PubMed ID: 9118157.
    Abstract:
    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.
    [Abstract] [Full Text] [Related] [New Search]