Age-related changes to cardiac systolic and diastolic function during whole-body passive hyperthermia

Abstract

What is the central question of this study? The effect of ageing on hyperthermia-induced changes in cardiac function is unknown. What is the main finding and its importance? Using echocardiography, we show that during hyperthermia the systolic and diastolic function can be appropriately augmented to meet cardiac demand in healthy older adults, although overall age-related impairments remain. One exception was late diastolic ventricular filling [i.e. E/A ratio and A/(A + E) ratio], which in the older adults was not further augmented during hyperthermia, unlike their young counterparts. To meet cardiac demand, therefore, healthy older adults appear to depend on an increased left ventricular systolic strain and proportion of their cardiac reserve. The effect of ageing on hyperthermia-induced changes in cardiac function is unknown. This study tested the hypothesis that hyperthermia-induced changes in left ventricular systolic and diastolic function are attenuated in older adults when compared with young adults. Eight older (71 ± 5 years old) and eight young adults (29 ± 5 years old), matched for sex, physical activity and body mass index, underwent whole-body passive hyperthermia. Mean arterial pressure (Finometer Pro), heart rate, forearm vascular conductance (venous occlusion plethysmography) and echocardiographic indices of diastolic and systolic function were measured during a normothermic supine period and again after an increase in internal temperature of ∼1.0 °C. Hyperthermia decreased mean arterial pressure and left ventricular end-diastolic volumes and increased heart rate to a similar extent in both groups (P > 0.05). Ageing did not alter the magnitude of hyperthermia-induced changes in indices of systolic (lateral mitral annular S' velocity) or diastolic function (lateral mitral annular E' velocity, peak early diastolic filling and isovolumic relaxation time; P > 0.05). However, with hyperthermia the global longitudinal systolic strain increased in the older group, but was unchanged in the young group (P = 0.03). Also, older adults were unable to augment late diastolic ventricular filling [i.e. E/A ratio and A/(A + E) ratio] during hyperthermia, unlike the young (P < 0.05). These findings indicate that older adults depend on a greater systolic contribution (global longitudinal systolic strain) to meet hyperthermic demand and that the atrial contribution to diastolic filling was not further augmented in older adults when compared with young adults.

Figure 1. Schematic overview of age-related and hyperthermia-induced changes to the cardiovascular system

Note that below the dotted line are echocardiographic responses. Novel findings from the present study are denoted with an asterisk (*).

Figure 2. Systolic annular velocities (S′) and peak global longitudinal systolic strain in young and older adults in normothermic and hyperthermic conditions

Individual and group-averaged echocardiographic data. Hyperthermia increased global longitudinal systolic strain (GLSS) in the older adults while remaining unchanged in the young, indicating an increased reliance on systolic mechanisms in the older adults. ^*Significant main effect of thermal condition, P < 0.05. ^†Significant main effect of age, P < 0.05. ^‡Significant post hoc pairwise comparison between age groups within thermal condition, P < 0.05.

Figure 3. Left ventricular end-diastolic volumes [absolute (in millilitres), left; and relative to body surface area (in millilitres per square metre), right] in young and older adults in normothermic and hyperthermic conditions

Individual and group-averaged echocardiographic data. Left ventricular end-diastolic volumes were unchanged by hyperthermia in both the young and older adults. ^*Significant main effect of age, P < 0.05.

Figure 4. Indices of early diastolic function in young and older adults in normothermic and hyperthermic conditions

Individual and group-averaged echocardiographic data of early diastole mitral annular velocities (E′) and mitral inflow velocity (E) during early diastolic filling. Hyperthermia did not change septal or lateral mitral annular velocities or peak mitral inflow velocity during early diastolic filling in young or older adults. ^*Significant main effect of age, P < 0.05. TDI, Tissue Doppler imaging.

Figure 5. Early propagation velocity of mitral inflow (V_p) and isovolumetric relaxation time (IVRT) in young and older adults in normothermic and hyperthermic conditions

Individual and group-averaged echocardiographic data. The IVRT shortened and V_p increased during hyperthermia in both young and older adults, indicating an increased rate of relaxation and suction for the left ventricle. ^*Significant main effect of thermal condition, P < 0.05. ^†Significant main effect of age, P < 0.05.

Figure 6. Indices of late diastolic ventricular filling in young and older adults in normothermic and hyperthermic conditions

Individual and group-averaged echocardiographic data of mitral annular velocities during late (A′) diastole and peak mitral inflow velocity during atrial contraction (A). Hyperthermia increased lateral A′ mitral inflow velocity and augmented A in both young and older adults, indicating an increased left atrial contribution to late diastolic filling. ^*Significant main effect of thermal condition, P < 0.05. ^†Significant main effect of age, P < 0.05.

Figure 7. The ratio of early and late mitral inflow velocities during diastolic filling (E/A ratio; left) and the contribution of atrial contraction to diastolic filling (right) in young and older adults in normothermic and hyperthermic conditions

Individual and group-averaged echocardiographic data. ^*Significant post hoc pairwise comparison between age groups within thermal condition, P < 0.05. ^†Significant post hoc pairwise comparison between thermal condition within age groups, P < 0.05.