Effects of Age, Sex and Isometric Exercise on Ventricular-Vascular Interactions During Cardiac Unloading

As people get older, especially women, they often feel dizzy or even faint when they go from sitting or lying down to standing up. This happens because their blood pressure (BP) drops, which can lead to falls, heart problems, and even death in older adults. When BP changes, it affects how well the heart works and how it talks with blood vessels. However, little research has been done on how the heart and blood vessels talk during times of low BP. The crosstalk between the heart and blood vessels is important, as it allows enough blood and oxygen to reach the brain and other vital organs. Some research shows that as we get older, the crosstalk does not work as well. This can make it harder for blood to flow properly or put extra pressure on the heart and arteries. That's why we want to study how the heart and blood vessels talk during a laboratory-simulated situation of low BP in young and older men and women. In our study, participants will lie down with their lower body in a chamber that creates a vacuum around their legs. This safely mimics what happens when you stand up quickly. We can then measure heart function, the stress on arteries, and BP while your legs are in that vacuum. We'll use an ultrasound to check the heart and a finger cuff to measure BP. We'll also see if gripping something firmly can help protect from sudden drops in blood pressure. This study will help us understand more about a condition called orthostatic hypotension and might even suggest that handgrip exercise could prevent it. The main questions the current study aims to address are: * Does the cross-talk between the heart and vessels become more impaired with aging during laboratory-simulated conditions of low BP? * Do women have worse crosstalk between the heart and blood vessels during laboratory-simulated conditions of BP? * Does hand gripping protect against drops in BP during conditions of low BP? All participants will be asked to * Complete two laboratory conditions on two separate days with a randomized order (like flipping a coin): * Exposure to a lower body negative pressure (LBNP) chamber to safely simulate low BP (control) * Exposure to a lower body negative pressure (LBNP) while conducting hand-squeezingexercise (experimental). The investigators will examine how heart and blood vessel interactions, as well as blood pressure (BP) responses, differ in young and older adults of both sexes when exposed to a laboratory-simulated low BP condition (LBNP), both with and without hand squeezing exercise.