Challenges to the Cardiovascular System II

Comparison of Resistance and Endurance Training Responses

• Foundational Principle: Resistance exercise alone does not improve the functional capacity of the cardiovascular system ($CVS$).
• Study Data on Left Ventricular (LV) Dimensions: Morganroth et al. (Ann J. Intern Med 1975) compared cardiac parameters across different athletic profiles ($n = 57$ subjects total):     * Untrained ($n = 16$):         * $LV\text{ mass}: 211\,g$         * $LV\text{ wall}: 10.3\,mm$         * $LV\text{ vol}: 101\,ml$         * $SV\text{ (Stroke Volume)}: (70)\,ml$     * College runners ($n = 15$):         * $LV\text{ mass}: 302\,g$         * $LV\text{ wall}: 11.3\,mm$         * $LV\text{ vol}: 160\,ml$         * $SV: 116\,ml$     * World class runners ($n = 10$):         * $LV\text{ mass}: 283\,g$         * $LV\text{ wall}: 10.8\,mm$         * $LV\text{ vol}: 154\,ml$         * $SV: 113\,ml$     * College wrestlers ($n = 12$):         * $LV\text{ mass}: 330\,g$         * $LV\text{ wall}: 13.7\,mm$         * $LV\text{ vol}: 110\,ml$         * $SV: 75\,ml$     * World class shot putters ($n = 4$):         * $LV\text{ mass}: 348\,g$         * $LV\text{ wall}: 13.8\,mm$         * $LV\text{ vol}: 122\,ml$         * $SV: 68\,ml$

Detraining and the 'Use It or Lose It' Principle

• Coyle EF et al. (1984) Study: Examined the time course of loss of adaptations after stopping prolonged intense endurance training.     * Subject Profile: Runners or cyclists who trained for $10$-$12$ months.     * Training Protocol: $5 imes 1\text{ hour sessions/week}$ at $70$-$80\%$ $VO_2 ext{max}$.     * Observation Period: Cardiovascular variables were monitored over $84\text{ days}$ of detraining after cessation of regular exercise.     * Results:         * Heart Rate ($HR$) increased.         * All other measured variables decreased: Cardiac Output ($CO$), Stroke Volume ($SV$), $O_2$ extraction, and $VO_2 ext{max}$.
• Kemi et al. (2004) Findings: Aerobic fitness is directly associated with cardiomyocyte contractile capacity and endothelial function during both training and detraining phases.

Cardiovascular Adaptations in Extreme Environments: Space and Bed Rest

• Cardiac Atrophy: Prolonged bed rest and spaceflight lead to cardiac atrophy (Perhonen et al., 2001).
• Comparative Metrics (Pre-flight vs. In-flight):     * Pre-flight (supine):         * $HR: 61 \pm 2\,bpm$         * $SV: 131 \pm 2\,ml$         * $CO: 8.0 \pm 0.2\,L/min$     * In-flight:         * $HR: 70 \pm 5\,bpm$         * $SV: 93 \pm 2\,ml$         * $CO: 6.5 \pm 0.4\,L/min$

Physiological vs. Pathological Cardiac Hypertrophy

• Functional (Physiological) Hypertrophy:     * Normal adaptation of the heart to chronic pressure or volume overload.     * Result: Improved cardiac function.
• Pathological (Pathophysiological) Hypertrophy:     * Maladaptation of the heart resulting in decreased cardiac work and increased afterload.     * Origins: Can be congenital (e.g., hypertrophic cardiomyopathy) or acquired (e.g., hypertension).     * Progression: Initially acts as a compensation for reduced cardiac function; however, it leads to an increase in cardiac work and ultimately results in cardiac failure.

Pathophysiological Challenges to Cardiovascular Function

• Reduced Blood Volume (Preload reduction):     * Haemorrhage.     * Burns.     * Diarrhoea/Vomiting.     * Dehydration.
• Reduced Venous Return (Preload reduction):     * Sepsis.     * Anaphylaxis.     * General Anaesthesia.
• Pump Dysfunction (Increased Afterload / Reduced Emptying):     * Systemic hypertension.     * Arrhythmia.     * Myocardial infarction ($MI$).     * Heart failure.     * Valve disease.

Consequences of Inadequate Cardiac Output and Mortality Statistics

• Primary Systemic Effects:     * Inadequate $O_2$ distribution and $CO_2$ removal.     * Hypotension and circulatory collapse.
• UK Mortality Data (ONS/The Guardian):     * Circulatory Diseases (Total): $158,084$ deaths ($-1.1\%$     * Specific Circulatory Causes:         * Cerebrovascular diseases (brain haemorrhage): $43,363$         * Chronic ischaemic heart disease: $43,957$         * Acute myocardial infarction (heart attack): $25,960$         * Other heart diseases: $24,718$         * High blood pressure (hypertensive): $4,726$         * Diseases of arteries, arterioles, and capillaries: $10,029$         * Diseases of veins, lymphatic vessels, and lymph nodes: $4,094$         * Chronic rheumatic heart diseases: $934$     * Non-Circulatory Comparisons:         * Cancer: $141,446$ ($+0.7\%$         * Respiratory diseases: $30,857$         * Bronchitis, emphysema, and chronic lung disease: $23,870$         * Diabetes: $5,223$

Heart Transplantation and Upregulation of Cardiac Output during Exercise

• Surgical Connections: A donor heart is installed by connecting the Aorta, Pulmonary artery, Superior vena cava, and Inferior vena cava.
• Control Mechanisms for Cardiac Output Upregulation:     1. Input from 'central command'.     2. Decreased parasympathetic activity.     3. Increased sympathetic activity.     4. Autonomic reflexes.     5. Direct effects of local signals: temperature, $pH$, $O_2$, $CO_2$, adenosine, $NO$, $Mg^{2+}$, $K^+$.     6. Feedback from activation of receptors in joints and muscles at the onset of exercise.
• Analytical Question: Students are prompted to consider what cardiovascular changes would occur specifically in a heart-transplant recipient (whose heart is denervated) during exercise.

VO2 Max: Aerobic Capacity and Determinants

• Definition: The maximum ability of the body to utilize oxygen during exercise. It serves as an indicator of maximum aerobic capacity ($ATP$ synthesis).
• Limiting Factors:     * The combined ability of the cardiovascular and pulmonary systems to transport oxygen to the muscular tissue system.     * The chemical ability of the muscular cellular tissue system to use oxygen in breaking down fuels.
• Metabolic Demand Pathway: Ventilation $\rightarrow$ Diffusion across respiratory membrane $\rightarrow$ Pulmonary blood flow $\rightarrow$ Carriage of gases by blood $\rightarrow$ Systemic blood flow $\rightarrow$ Blood tissue gas exchange.
• Determinants of $VO_2\text{max}$:     * Training status.     * Gender.     * Size, stature, and body composition.     * Heredity.     * Muscle fibre type.     * Haematocrit.
• $VO_2\text{max}$ Ranges for International Athletes ($ml \cdot kg^{-1} \cdot min^{-1}$):     * Cross-country skiing: Men $69$-$95$, Women $56$-$74$.     * Long-distance running: Men $65$-$80$, Women $55$-$72$.     * Rowing: Men $58$-$74$, Women $48$-$68$.     * Cycling: Men $56$-$72$.     * Football: Men $54$-$70$, Women $48$-$68$.     * Figure skating: Men $42$-$54$.     * Untrained: Men $38$-$52$, Women $30$-$46$.
• Correlation with Cardiac Output: There is a close linear relationship between maximal cardiac output ($CO\text{max}$) and maximal oxygen consumption ($VO_2\text{max}$). Values for sedentary individuals typically cluster around $14$-$22\,L/min$ $CO$ and $2.0$-$3.0\,L/min$ $VO_2$, while endurance athletes can reach $38$-$40\,L/min$ $CO$ and $5.0$-$6.0\,L/min$ $VO_2$.