BCR TBL 13 - Control of Breathing, Pulmonary Circulation & Hypoxaemia

What is the primary driver of ventilation in healthy individuals?

Increased PaCO₂

Where are central chemoreceptors located?

Medulla oblongata

What do central chemoreceptors respond to?

Changes in CSF pH due to CO₂

Where are peripheral chemoreceptors found?

Carotid and aortic bodies

What stimulates peripheral chemoreceptors most strongly?

PaO₂ < 60 mmHg

Which nerve carries information from the carotid body?

Glossopharyngeal nerve (CN IX)

Which nerve carries information from the aortic body?

Vagus nerve (CN X)

What is Type I respiratory failure defined by?

Low PaO₂, normal or low PaCO₂

What is Type II respiratory failure defined by?

Low PaO₂ and high PaCO₂

Name a common cause of Type I respiratory failure.

Pneumonia, pulmonary embolism, ARDS

Name a common cause of Type II respiratory failure.

COPD, opioid overdose, neuromuscular disease

What happens to ventilation during sleep?

It decreases

What is the mechanism of obstructive sleep apnea?

Upper airway collapse during sleep

What is the mechanism of central sleep apnea?

Absent central respiratory drive

Name one consequence of obstructive sleep apnea.

Daytime sleepiness, cardiovascular disease

What is pulmonary hypertension defined as?

Pulmonary artery pressure >25 mmHg at rest

What is cor pulmonale?

Right heart failure secondary to lung disease

What commonly causes cor pulmonale?

Chronic hypoxia from COPD or ILD

What is the normal arterial blood pH range?

7.35–7.45

What is the normal PaCO₂ range?

35–45 mmHg

What is the normal HCO₃⁻ range?

22–26 mEq/L

What is base excess?

A measure of metabolic component of acid-base status

What acid-base imbalance results from opioid overdose?

Respiratory acidosis

What acid-base imbalance is seen in vomiting?

Metabolic alkalosis

What acid-base disturbance occurs in diarrhea?

Metabolic acidosis

What acid-base imbalance occurs in hyperventilation?

Respiratory alkalosis

What is the compensation for respiratory acidosis?

Renal HCO₃⁻ retention

What is the compensation for metabolic acidosis?

Respiratory (↑ ventilation to blow off CO₂)

What is the compensation for respiratory alkalosis?

Renal HCO₃⁻ excretion

What is the compensation for metabolic alkalosis?

Hypoventilation to retain CO₂

What happens to PaCO₂ in metabolic acidosis?

It decreases (respiratory compensation)

What causes increased erythropoietin at high altitude?

Hypoxia

What is the immediate ventilatory response to high altitude?

Hyperventilation

What does increased 2,3-DPG at altitude do?

Facilitates O₂ unloading at tissues

What happens to PaCO₂ during acclimatization?

Decreases

What happens to pH initially at altitude?

Increases (respiratory alkalosis)

What are long-term adaptations to high altitude?

↑ RBC mass, ↑ 2,3-DPG, ↑ capillary density

What causes high-altitude pulmonary edema (HAPE)?

Hypoxia-induced pulmonary vasoconstriction

What is hypoxaemia?

Low arterial PaO₂

What is the effect of hypoxia on pulmonary vessels?

Vasoconstriction

What is the effect of hypoxia on systemic vessels?

Vasodilation

What is the difference in pressure between systemic and pulmonary circulation?

Systemic is high pressure; pulmonary is low pressure

What is the difference in resistance between systemic and pulmonary circulation?

Systemic has higher resistance

What happens to pulmonary blood flow during exercise?

Increases via capillary recruitment and distension

What is the V/Q response during exercise?

It improves due to better perfusion

What is the effect of posture on pulmonary perfusion?

Perfusion increases in dependent lung regions

What is the Hering–Breuer reflex?

Lung stretch inhibits inspiration

Which area of the brainstem sets the basic respiratory rhythm?

Pre-Bötzinger complex in medulla

What does the dorsal respiratory group (DRG) control?

Inspiration

What does the ventral respiratory group (VRG) control?

Expiration (especially during forced breathing)

What part of the brain modulates respiratory rate and rhythm?

Pons (apneustic and pneumotaxic centers)

What is Cheyne–Stokes respiration?

Periodic breathing with crescendo-decrescendo pattern

What condition is Cheyne–Stokes associated with?

Heart failure or brain injury

What happens to ventilation response to CO₂ during sleep?

It decreases

What happens to upper airway muscle tone during REM sleep?

It decreases

What is a typical oxygen saturation in obstructive sleep apnea?

Desaturation episodes <90%

What is a treatment for obstructive sleep apnea?

CPAP (continuous positive airway pressure)

What condition involves absent effort to breathe during apnea?

Central sleep apnea

What is a cause of central sleep apnea?

Opioid use, stroke, heart failure

What is the treatment for central sleep apnea?

Adaptive servo-ventilation, treat underlying cause

What is base deficit?

A negative base excess indicating metabolic acidosis

What is the alveolar gas equation used to calculate?

Alveolar PaO₂

What is the normal A-a gradient?

<15 mmHg in young adults

What conditions increase the A-a gradient?

V/Q mismatch, diffusion impairment, shunt

What conditions do not increase the A-a gradient?

Hypoventilation, high altitude

What is the effect of anemia on PaO₂?

None; oxygen content is reduced, not PaO₂

What is the Bohr effect?

Rightward shift of O₂ dissociation curve with ↑ CO₂, ↓ pH

What is the Haldane effect?

Deoxygenated blood carries more CO₂

What happens to cerebral blood flow in hypercapnia?

It increases

What happens to cerebral blood flow in hypocapnia?

It decreases (vasoconstriction)

What is respiratory quotient (RQ)?

CO₂ produced / O₂ consumed (~0.8)

What is the function of pulmonary stretch receptors?

Inhibit inspiration when lungs inflate

What stimulates J receptors in lungs?

Pulmonary congestion, leading to rapid shallow breathing

What stimulates irritant receptors?

Smoke, dust → cough reflex

What is the oxygen-hemoglobin dissociation curve?

Relationship between PaO₂ and hemoglobin saturation

What shifts the curve to the right?

↑ CO₂, ↑ temperature, ↓ pH, ↑ 2,3-DPG

What shifts the curve to the left?

↓ CO₂, ↓ temperature, ↑ pH, ↓ 2,3-DPG

What is the total oxygen content formula?

(1.34 x Hb x SaO₂) + (0.003 x PaO₂)

What is the partial pressure of inspired oxygen at sea level?

~150 mmHg (21% of 760 mmHg - water vapor)

What happens to oxygen diffusion in fibrosis?

It is impaired

What happens in pulmonary embolism?

Perfusion defect → high V/Q ratio

What is the most efficient V/Q ratio for gas exchange?

~0.8

What causes a shunt?

Blood bypassing alveoli (e.g., pneumonia, atelectasis)

What is dead space?

Air not participating in gas exchange (e.g., trachea)

What increases physiologic dead space?

Pulmonary embolism

What happens to CO₂ in hyperventilation?

It decreases → respiratory alkalosis

What happens to CO₂ in hypoventilation?

It increases → respiratory acidosis

What is a hallmark of respiratory acidosis?

Low pH, high PaCO₂

What is a hallmark of metabolic alkalosis?

High pH, high HCO₃⁻

What causes Kussmaul breathing?

Metabolic acidosis (e.g., DKA)

What is minute ventilation?

Tidal volume × respiratory rate

What is alveolar ventilation?

(Tidal volume - dead space) × respiratory rate

What increases minute ventilation?

Exercise, hypercapnia, hypoxia

What limits diffusion of gases in the lung?

Thickened alveolar membrane, decreased surface area

What is Fick's law?

Gas diffusion ∝ (area × ΔP) / thickness

What is the effect of CO₂ retention on acid-base status?

Causes respiratory acidosis

What is the effect of bicarbonate retention?

Causes metabolic alkalosis

Which part of the medulla contains the pre-Bötzinger complex?

Ventral respiratory group

What structure modulates inspiratory depth and rate in the pons?

Pneumotaxic center

What structure promotes prolonged inspiration in the pons?

Apneustic center