Age-dependent effects of thoracic and capillary blood volume distribution on pulmonary artery pressure and lungdiffusing capacity.

Kirsten E Coffman,Bruce D Johnson,Alex R Carlson,Matthew G Boeker

doi:10.14814/phy2.13834

Abstract

Aging is associated with pulmonary vascular remodeling and reduced distensibility. We investigated the influence of aging on changes in cardiac output (Q), mean pulmonary artery pressure (mPAP), and lung diffusing capacity in response to alterations in thoracic blood volume. The role of pulmonary smooth muscle tone was also interrogated via pulmonary vasodilation. Nine younger (27 ± 4 years) and nine older (71 ± 4 years) healthy adults reached steady‐state in a Supine (0°), Upright (+20°), or Head‐down (−20°) position in order to alter thoracic blood volume. In each position, echocardiography was performed to calculate mPAP and Q, and lung diffusing capacity for carbon monoxide (DLCO) and nitric oxide (DLNO) was assessed. Next, 100 mg sildenafil was administered to reduce pulmonary smooth muscle tone, after which the protocol was repeated. mPAP (P ≤ 0.029) and Q (P ≤ 0.032) were lower in the Upright versus Supine and Head‐down positions, and mPAP was reduced following sildenafil administration (P = 0.019), in older adults only. SV was lower in the Upright versus Supine and Head‐down positions in both younger (P ≤ 0.008) and older (P ≤ 0.003) adults. DLCO and DLNO were not greatly altered by position changes or sildenafil administration. However, the DLNO/DLCO ratio was lower in the Supine and/or Head‐down positions (P ≤ 0.05), but higher following sildenafil administration (P ≤ 0.007), in both younger and older adults. In conclusion, older adults experience greater cardiopulmonary alterations following thoracic blood volume changes, and pulmonary smooth muscle tone plays a role in resting mPAP in older adults only. Furthermore, mPAP is an important determinant of pulmonary capillary blood volume distribution (DLNO/DLCO), regardless of age.

Highlights

There was no change in Supine values of mean pulmonary artery pressure (mPAP) following sildenafil administration (Fig. 1; pre 15.4 Æ 1.6 vs. post 15.5 Æ 1.6 mmHg, P = 0.327; Dsildenafil = 0.03 Æ 0.7 mmHg)
In older adults mPAP was lower in the Upright versus Supine and Head-down positions both pre-sildenafil (Fig. 1; Upright 16.1 Æ 2.1 vs. Supine 18.4 Æ 3.4 mmHg, P = 0.022 and Head-down 18.9 Æ 3.4 mmHg, P = 0.029) and post-sildenafil (Fig. 1; Upright 14.9 Æ 1.9 vs. Supine 16.1 Æ 2.1 mmHg, P = 0.013 and Head-down 17.4 Æ 2.6 mmHg, P = 0.007)
MPAP was decreased in the Supine position following sildenafil administration

Summary

Introduction

Aging is associated with remodeling of the pulmonary artery and vein (Fernie and Lamb 1986; Harris et al 1965; Hosoda et al 1984; Mackay et al 1978; Plank et al 1980; Warnock and Kunzmann 1977) and a reduction in pulmonary vascular distensibility as assessed by ex vivo methods (Banks et al 1978; Gozna et al 1974; Harris et al 1965; Mackay et al 1978; Reeves et al 2005). Physiological Reports published by Wiley Periodicals, Inc. on behalf of The Physiological Society and the American Physiological Society We sought to use a simple, noninvasive method at rest in order to assess age-dependent differences in variables that are related to pulmonary vascular distensibility. We used passive changes in body position to investigate the age-dependent responses of mean pulmonary artery pressure (mPAP) and cardiac output (Q) in healthy individuals

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Discussion

Conclusion