Cardiopulmonary, Metabolic, Renal & Hepatic Physiology – Key Vocabulary

Cardiovascular Responses to Acute Aerobic Exercise

Cardiac Output, Heart Rate, Stroke Volume

• Fundamental relationship: Q = HR \times SV
  • "Q" (cardiac output) represents the volume of blood pumped per minute.
  • HR (heart rate) and SV (stroke volume) are the principal determinants.
• Exercise Effects
  • HR rises almost linearly with %VO₂max until approaching maximal levels.
  • Question posed in lecture: "What is the implication for HR excursion if SV plateaus at a higher % of VO₂max?"
    • If SV plateaus early, HR must do more of the work to elevate Q → larger HR excursion.
  • SV increases sharply at exercise onset, then plateaus (~40–60 % VO₂max in untrained; higher in trained).
• Rating of Perceived Exertion (RPE)
  • Strong positive correlation with HR during sub-max and max work.
  • Practical use: RPE can estimate HR when direct measurement isn’t feasible.

Blood Pressure & Total Peripheral Resistance (TPR)

• Core equation: MAP = Q \times TPR
• Systolic BP (SBP)
  • Rises proportionally to workload (≈10 mm Hg per MET for healthy adults).
  • Mechanisms
  • ↑ Myocardial contractility.
  • ↑ SV → ↑ Q.
  • Muscles demand higher driving pressure to receive blood.
• Diastolic BP (DBP)
  • Shows minimal change (±10 mm Hg) during dynamic exercise.
  • Mechanism: arteriolar vasodilation within active muscle allows more runoff from arterial tree.
• TPR
  • Falls because vasodilation in active beds > vasoconstriction in non-active beds.
• Dynamic vs. Static Exercise BP Profiles
  • Dynamic (cyclic) work → large ↑ SBP, little DBP change.
  • Static (isometric) work → SBP & DBP both rise substantially because muscle contraction compresses vessels, impeding flow.

Blood Flow Redistribution

• Rest: ~15–20 % of Q to skeletal muscle.
• Heavy exercise: 80–85 % to muscle.
• Governing forces
  • Sympathetic nervous system (SNS) & circulating epinephrine (EPI) → systemic vasoconstriction.
  • Local metabolites (↑PCO2, ↓PO2, ↑[H⁺], adenosine, ↑[K⁺], nitric oxide) → functional sympatholysis → vasodilation in working muscle.
  • Result: Overall vasoconstriction maintains MAP while local dilation supplies muscle.
• Capillary Recruitment
  • More open capillaries increase surface area for exchange, lower diffusion distance.
• Question posed: "Why doesn’t MAP decrease during exercise?"
  • ↑ Q offsets ↓ TPR, maintaining or slightly elevating MAP.

Summary of Acute CV Responses

• ↑ Q, HR, SV.
• ↑ SNS activity & catecholamines (NE/EPI).
• ↑ Venous return (muscle pump, respiratory pump).
• Vasodilation in active tissue; vasoconstriction in inactive beds.
• Goal: Match O₂ delivery to metabolic demand.

Chronic Cardiovascular Adaptations to Aerobic Training

Left-Ventricular (LV) Remodeling

• Eccentric hypertrophy: ↑ sarcomere number/length → ↑ LV internal volume (preload).
• Outcomes
  • ↑ SV at rest & sub-max → ↓ resting HR for same Q.
  • ↑ Max SV allows greater Qmax without change in HRmax.

Blood Volume Adaptations

• ↑ Plasma Volume (PV) (≈10–20 % within weeks).
  • Drives ↑ SV via ↑ EDV (Frank-Starling).
  • Benefit for thermoregulation: larger PV supports sweating without compromising venous return.
• ↑ Red Blood Cell mass via erythropoiesis → maintains/raises Hct despite hemodilution.

Vascular Adaptations

• ↑ Capillary density in muscle → greater O₂ extraction.
• ↑ Endothelial release of nitric oxide, K⁺, adenosine → better local control.
• ↓ Afterload (arterial stiffness, systemic BP) → augments SV.

Pulmonary & Ventilatory Responses

Ventilation ((\dot V_E))

• Increases linearly with work rate until reaching the Ventilatory Threshold (VT) at ~50–75 % VO₂max.
  • Post-VT → exponential rise.
  • On-set/Off-set kinetics mirror Q.
• Ventilatory Breakpoint
  • Disproportionate ↑ \dot V_E relative to VO₂ due to metabolic acidosis (↑[H⁺], ↑CO₂) → chemoreceptor stimulation.
  • VT ≈ Anaerobic Threshold but measured non-invasively.

Factors Elevating Ventilation at VT

• ↑ Blood [CO₂], [H⁺], [K⁺].
• ↑ Blood temperature & catecholamines.
• ↑ Central motor command/motor-unit recruitment.

(a-v)O₂ Difference

• Widens with intensity because muscles extract more O₂ (↑ mitochondrial O₂ use, ↑ capillary density).

Metabolic Foundations

Respiratory Exchange Ratio (RER)

• Definition: RER = \frac{VCO2}{VO2} (steady-state requirement).
• Interpretations
  • RER \approx 0.70 → predominately fat oxidation.
  • RER \approx 1.00 → predominately CHO oxidation.
  • RER = 0.85 → ~50 % fat / 50 % CHO.
  • RER > 1.00 → hyperventilation & bicarbonate buffering; indicates near-max effort.

Fuel Stores (≈80 kg adult male)

• Carbohydrates ≈ 2,012 kcal (liver glycogen 400, muscle glycogen 1,600, blood glucose 12).
• Fat ≈ 110,740 kcal (subcutaneous, intramuscular, plasma).

Energy Systems & ATP Resynthesis

• ATP-PCr (phosphagen) – immediate, cytosolic.
• Glycolytic (anaerobic) – cytosolic, 1–2 min dominant, produces lactate.
• Oxidative – mitochondrial, sustained energy.

Lactate (Ventilatory) Threshold (LT/VT)

• Exercise intensity at which blood [lactate] or \dot V_E rises non-linearly.
• Relevance
  • Athletic: predicts endurance race pace; training (tempo, intervals) aims to shift LT rightward.
  • Clinical: deconditioned patients reach LT at low workloads → early fatigue; PT can use graded activity to elevate LT.

Nutrients

• Six classes: CHO, fat, protein, vitamins, minerals, water.
• Roles: energy (CHO/fat), structure (protein, Ca, P), regulation (vit/min/protein).
• Energy yields: CHO & protein = 4 kcal g⁻¹, fat = 9 kcal g⁻¹.

Ancillary Pathways

• Glycogenolysis, Glycogenesis, Gluconeogenesis, Lipolysis, Lipogenesis, Proteolysis.

Renal Physiology & Pathophysiology

Nephron Anatomy

• ~1 million per kidney; functional unit.
• Components
  • Renal corpuscle = glomerulus + Bowman’s capsule (filtration).
  • Tubule segments: PCT, loop of Henle (descending/ascending), DCT, collecting ducts.
• Blood flow path: Aorta → renal artery → segmental → interlobar → arcuate → cortical radiate → afferent arteriole → glomerulus → efferent arteriole → peritubular/vasa recta → venous return.

Kidney Functions (Regulation Theme)

• Fluid & electrolyte balance, acid–base balance.
• BP regulation (renin–angiotensin–aldosterone, volume control).
• Erythropoietin & thrombopoietin production.
• Bone metabolism (vitamin D activation, Ca²⁺/PO₄³⁻ handling).
• Excretion of wastes, toxins, drugs.

Urine Formation Processes

• Filtration in glomerulus.
• Secretion in tubules/collecting ducts.
• Reabsorption along nephron.
• Overall: \text{Excretion} = \text{Filtration} + \text{Secretion} - \text{Reabsorption}.

Cardio-Renal Interrelation

• Chronic HTN → 2nd leading cause of CKD.
• CKD → volume overload, anemia, and ↑ cardiovascular morbidity.

Kidney Failure

• Acute Renal Failure (ARF): sudden, reversible if treated; causes – ischemia, toxins, obstruction.
• Chronic Renal Failure (CRF): progressive → End-Stage Renal Disease (ESRD); causes – diabetes, HTN, lupus, obstruction.
• Uremia: toxic accumulation of nitrogenous waste → anorexia, nausea, cognitive changes; dialysis/transplant required.

Abdominal Quadrants & Visceral Anatomy

RUQ

• Liver (right lobe), gallbladder, portions of colon & small intestine, right kidney.

RLQ

• Appendix, lower ascending colon, small intestine, right ureter/ovary/spermatic cord.

LUQ

• Stomach, spleen, pancreas, liver (left lobe), left kidney, transverse/descending colon.

LLQ

• Descending colon, small intestine, left ureter/ovary/spermatic cord.

Hepatic Physiology & Disease

Liver Overview

• ~2.5 % body mass, only organ that regenerates.
• Dual supply: 25–30 % hepatic artery, 70–75 % portal vein.
• 70–80 % cells = hepatocytes.

Multifunctional Roles

• Drug detoxification (penicillin, erythromycin, sulfonamides, etc.).
• Hormone metabolism (thyroxin, aldosterone, estrogen, cortisol, insulin, glucagon, GH, GI hormones).
• Energy metabolism
  • Glycogen storage & breakdown (glycogenolysis).
  • Gluconeogenesis, ketogenesis.
  • Triglyceride storage.
• Protein synthesis (albumin, clotting factors) & micronutrient handling.
• Immune contribution (Kupffer cells).

Pancreas Functions

• Endocrine (≈5 %)
  • Insulin → ↑ glucose uptake.
  • Glucagon → glycogenolysis ↑ blood glucose.
  • Somatostatin → inhibits both insulin & glucagon.
• Exocrine (≈95 %)
  • Digestive enzymes: trypsin family (proteins), amylase (CHO), lipase (fats), nucleases (DNA/RNA).
  • Bicarbonate secretions neutralize chyme.

Referred Pain Patterns

• Esophagus ↔ mid-thoracic spine.
• Liver/diaphragm/pericardium ↔ shoulder.
• Stomach, gallbladder, pancreas, small intestine ↔ mid-back, scapular region.
• Colon, appendix, pelvic viscera ↔ low back, pelvis, sacrum.
• Spleen ↔ left shoulder (Kehr’s sign) & left Abd; can impair breathing.

Hepatitis

• HAV
  • Fecal–oral, food/water; acute only; vaccine available.
• HBV
  • Blood & body fluid transmission; vaccine available; can co-infect with HDV (worse prognosis).
• Prevention strategies: hygiene, PPE, needle protocols, immunization.

Cirrhosis

• Irreversible fibrosis from chronic hepatitis, alcohol, etc.
• Signs/Sx
  • Jaundice, peripheral edema, hepatosplenomegaly, ascites.
  • Dupuytren’s contracture (4th/5th digit), palmar erythema (↑ estradiol), spider angiomas.

Clinical & Practical Connections

• PTs must monitor SBP responses (drop or excessive rise = termination criteria).
• RPE & talk/sing tests provide low-tech intensity gauges: easy to sing → below LT; can’t talk → above LT.
• Chronic deconditioning lowers LT & VT → patients fatigue with ADLs; progressive aerobic training shifts thresholds right.
• Knowledge of referred pain critical for differential diagnosis (e.g., shoulder pain of hepatic origin).