Lecture 8 Dr. Zahoor Ali Shaikh 1

Alveolar Ventilation increases 20-fold during heavy exercise to keep pace with increased demand of O 2 uptake and CO 2 output. Big three chemical factors that is decreased P O 2, increased P CO 2 and increased H+ does not play major role. During exercise, ventilation increases at the onset of exercise within seconds, long before arterial blood gases could become important which requires minutes. 2

Reflexes originating from joints and muscle receptors during exercise reflexly stimulate the respiratory center. Increase in body temperature during exercise stimulates ventilation. Increased Epinephrine release during exercise stimulates ventilation. Impulses from cerebral cortex, at the onset of exercise stimulates medullary respiratory neuron. 3

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Respiratory rate and depth can be modified by 1. Sneezing & Coughing – these are protective reflexes to expel irritant material. 2. Pain - anywhere in the body reflexly stimulate respiration. 3. Laughing, crying modifies the respiration. 5

4. Hiccups – Spasmodic contraction of the diaphragm occurs, causing rapid intake of air which is suddenly halted by abrupt closure of glottis. 5. Swallowing – reflexly inhabits respiratory center to prevent food from entering the lungs. 6. Speaking, singing, and whistling: We also control our breathing to perform such voluntary acts. 6

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Cyanosis is a blue coloration of skin and mucous membranes. It results when reduced Hemoglobin in capillary blood is more than 5g/100ml of blood. Central Cyanosis occurs in severe hypoxia in lung disease, Right to left shunt eg Ventricular septal defect. 9

Types of Hypoxia are given in the Slide 7 [Table 13-7]. Here is the example for each type of Hypoxia. Hypoxic Hypoxia occurs in lung disease, at high altitude. Anemic Hypoxia occurs in Anemia and CO Poisoning. Circulatory Hypoxia or Stagnant Hypoxia occurs in slow circulation e.g. Cardiac failure. Histotoxic Hypoxia occurs when tissues are not able to use O 2. It occurs in Cyanide Poisoning. 10

Apnea is the transient interruption of ventilation, with breathing resuming spontaneously. If breathing does not resume, the condition is called respiratory arrest. During sleep ventilation is normally decreased and the central chemoreceptors are less sensitive to the arterial PCO2 drive, victims of sleep apnea may stop breathing for a 10 seconds or longer many times in the night. 11

Mild sleep apnea is not dangerous unless the sufferer has pulmonary or circulatory disease, which can be exacerbated by recurrent bouts of apnea. 12

In SIDS, Apnea occurs [stoppage of breathing] and patient is unable to recover from Apnea period and death occurs. SIDS or crib [cot] death – It is the leading cause of death in the first year of life, usually 2-4 months old infant is found dead in his or her cot for no apparent reason. 13

 Cause is not clear but different possibilities are put forward: Baby forgets to breath – as respiratory control mechanism are immature either in brain stem or chemoreceptors are poorly developed. Abnormal lung development. Aspiration of gastric [stomach] juice containing Helicobacter pylori. Combination of factors maybe involved. 14

 Other Observations In SIDS Sleeping position of baby – 40% increased incidents of SIDS is associated with sleeping on the abdomen rather than on the back or side. Infants whose mother smoked during pregnancy are more likely to die of SIDS. 15

pH of blood – 7.4 [ ] Lungs and kidneys regulate the pH of body. Lungs play important role in regulation of pH because they excrete CO2. Respiratory Acidosis If respiratory center is depressed e.g. brain damage, drugs, it will increase CO2 in the body which will increase H+. CO2 + H2O  H2CO3  H + HCO3 If H+ ion increases – it will cause Respiratory Acidosis. 16

If person hyperventilates, it will cause loss of CO2 and H+ ions and pH becomes alkaline [respiratory alkalosis]. 17

Effect of Exercise on - O 2 use and CO 2 production - Alveolar Ventilation - Arterial P O2, Arterial P CO2, Arterial H+ level Clinically Important Respiratory States [Given in Table 13-7 Slide 7] Cyanosis Hypoxia Apnea Sudden Infant Death Syndrome [SIDS] Respiratory acidosis and alkalosis 18

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