Twenty-six physiological parameters to assess aging

Twenty-six physiological parameters to assess aging

Highlights:

• The aging process causes structural and functional changes in different organs and systems
• Physiological measures are parameters that are used to assess the changes taking place in various organs and systems
• The aging process influences many physiological parameters, causing most of them to decline as organs function decreases with time

Introduction

Physiological aging involves the progressive decline in organ and/or system function. Examples of the latter include neurological, pulmonary, cardiovascular, musculoskeletal, and other systems. The speed of function decline varies among individuals and organs themselves. They are attributed to reasons like genetics, environment, and developmental factors. Since there is an intra- and inter-individual variability in terms of physiological function, assessing these changes will help determine the extent of the decline in organs’ functional capacity. Collectively, these measures provide an idea about how the aging process impacts the overall health of individuals and guide interventions to combat age-related changes.

Image 1

Cardiovascular physiological measurements

The cardiovascular system is perhaps one of the most well-studied systems impacted by the aging process. In this context, research has shown that the cardiovascular system undergoes structural and functional changes due to aging (1). Examples of structural changes include increased vascular stiffness, ventricular thickness, and atrial size (2). These changes occur due to reduced elasticity, increased left atrial pressure, and other causes. The outcome is an increased risk of atherosclerosis, hypertension, stroke, and arrhythmia (2). Functional changes involve reduced nitric oxide production (supports many biological actions, like blood vessels widening) and reduced threshold for cell calcium overload (lower arrhythmia threshold and increased risk of myocyte death).

Several physiological parameters could be utilized to understand the impact of aging on the cardiovascular system. They are illustrated in the table below (3).

Functional parameter

Definition

Heart rate variability (HRV)

It is the fluctuation in time intervals between heartbeats. It decreases with aging, leading to an increased risk of coronary heart disease and mortality (4, 5).

Aortic valve calcification

A progressive condition characterized by the formation of calcium deposits on the aortic heart valve (6).

Augmentation index

It is the difference between the first and second peaks of the central arterial waveform. It is an indirect measure of systemic arterial stiffness. It increases with age (7).

Left ventricular mass

It is a strong predictor of adverse cardiovascular events. This parameter increases with age (8, 9).

Brachial pulse pressure

It is the difference between systolic and diastolic blood pressure. It increases with age and is an established marker of cardiovascular diseases (10).

Pulse-wave velocity

A clinically useful indicator of arterial stiffness. It is the speed at which pressure waves generated from systolic contractions move through the arteries (11).

Assessing the aging impact on pulmonary function

Lung function is a reliable physiological marker of aging. The literature indicates that aerobic capacity decreases by more than 20% per decade after 70 years (3). In the same context, research shows that the aging process alters the structure and function of the lung and supportive parts, like the chest wall and respiratory muscles (12). These changes trigger unfavorable lung mechanisms associated with increased air trapping, reduced gas exchange, and decreased expiratory airflow.

Lung function testing represents a helpful tool that determines the aging impact on the respiratory tract. The table below captures physiological pulmonary tests that could help assess lung health and how aging has impacted it (3, 13-22).

Functional parameter

Definition

Peak aerobic capacity (VO_2Peak)

Is the person’s capacity to maximize oxygen use while performing physical activity. It declines as individuals age. It decreases by 3-6% in the third and fourth decades of life.

Spirometry (FEV1, FVC, FEV1/FVC ratio)

A common pulmonary test that assesses fitness and monitors lung function. According to research, lung function declines with age.

Lung volumes (TLC, FRC, RV)

Lung volumes help monitor lung health over time. Changes in these volumes start to appear after the age of 35. For example, FRC increases with age due to reduced lung elasticity, making air harder to expel. RV and TLC also increase due to aging.

Diffusing capacity for carbon monoxide

It measures the lung's capacity to transfer carbon monoxide from inspired air into the bloodstream. It decreases with aging, but maintaining a healthy lifestyle and exercising could ease the decline.

Quantitative ventilation-perfusion scanning

It is an established parameter for lung function. The mismatch between ventilation/perfusion increases with age due to airway closure in certain parts of the lung.

FEV1: Forced expiratory volume in the first second; FVC: Forced vital capacity; TLC: Total lung capacity; FRC: Functional residual capacity; RV: Residual volume.

Image 2

Physiological measurements to assess the age-related impact on renal function

Under normal conditions, the kidneys are highly metabolic organs that are impacted by aging. According to the literature, the kidneys undergo structural and functional changes due to aging (23). For example, research highlights that kidney mass changes by up to 25% between the third and eighth decades of life. Nephrosclerosis (hardening of the wall lining small arteries and arterioles supplying the kidney), a hallmark of kidney aging, will cause the loss of up to 6500 nephrons (the structural and functional unit of the kidney. Each kidney has an average of 900,000 to 1 million nephrons) per year after the age of 30 (3, 23, 24). Also, the glomerular filtration rate (GFR) (a biomarker showing kidneys' filtration capacity or how well they work) falls by about 5–10 % per decade after the age of 35 years (23).

Several tests could be utilized to assess the impact of aging on renal function. They are listed below (3, 25).

Functional parameter

Definition

Creatinine clearance

It is the volume of plasma cleared of creatinine per time unit. Research shows that it declines with age.

Glomerular filtration Rate (GFR)

A test that is used to detect how well the kidneys function. Glomeruli are kidney structures that remove waste. GFR decreases with age.

Musculoskeletal system and physiological markers

Like other bodily systems, multiple players in the musculoskeletal system are affected by aging. For example, skeletal muscle mass and strength decline with aging (26). Also, tendons, bones, and cartilages are impacted by age.

There are several parameters that could be assessed to determine the overall impact of age on the musculoskeletal system. They are summarized in the following table (3, 27-31).

Functional parameter

Definition

Grip strength

A measure that is widely adopted as a useful indicator of overall strength. In addition to measuring grip strength, it assesses upper limb function, bone mineral density, presence of comorbidities, and others.

Unipedal stance test of balance

It is a test that is used to assess postural balance.

Grooved pegboard test of fine motor coordination

It is a test that measures fine-motor task speed on both sides of the body.

SF-36 physical functioning scale

A questionnaire that evaluates the overall quality of life by incorporating several measures, including physical functioning.

Gait speed

The walking test could serve as a subjective estimator of general health and skeletal muscle mass.

SF: Short form.

Image 3

Other physiological measurements

In addition to the measurements listed above, other systems and bodily functions are impacted by aging. Examples include the immune system, neurocognitive function, integumentary (skin and appendages) system, and sensory system (3).

The table below compiles a number of physiological measures that could help understand the impact of aging on different body parts by assessing these parameters (3, 32-41).

Functional parameter

Definition

Immune risk profile (immune system)

It assesses a cluster of parameters, including proteins CD4, CD8, CD19, and others. Elevations of this profile are associated with functional limitations and mortality in the elderly.

Mini-mental status examination (neurocognitive)

A test that is used to detect cognitive impairment. Research shows that test scores decrease with age.

Cognitive battery (neurocognitive)

It is a test that assesses key cognitive abilities, like attention, memory, and verbal fluency.

Visual acuity (sensory)

A test based on a chart containing 11 lines, with each line including letters of various sizes.

Auditory tests (sensory)

These are tests that assess age-related hearing loss.

Skin elasticity tests (integumentary system)

Tests to assess skin elasticity. They help identify age-related changes occurring to the skin. The literature indicates that skin elasticity decreases with aging.

Skin thickness (integumentary system)

Tests carried out to determine skin thickness, as research shows that it decreases with age.

Wrinkle parameters measurement (integumentary system)

Wrinkles increase due to multiple factors associated with aging, like collagen loss. Measuring wrinkles could help determine the impact of aging on the skin.

Conclusions

The aging process carries many changes to different body organs and systems. Research has established that the aging process causes a decline in the overall body function. There are physiological parameters that could help establish how far aging has impacted the body to capture these changes. Although these parameters may not be specifically established to understand the said impact, they provide a clear picture of how aging leads to changes in physiological parameters. Capturing and understanding the value of these physiological measurements could help establish how different biological age is from chronological age.

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