Blunted ventilatory response

Blunted Ventilatory Response to Hypoxia in High-Altitude Natives. 235... 

Human ventilatory responses to CO2 at different levels of PO2, decreasing levels of PO2 increased the response to CO2 (upper panel but not in the lower panel. The response to CO2 remains in the face of blunted response to hypoxia (From Milledge and Lahiri, 1967)... 

Undernourished patients have demonstrated a blunted response to hypercapnia that improves after as little as 1 week of adequate nutritional support. This response is thought to result from protein administration, as evidenced by decreased partial CO2 pressure, increased minute ventilation, and improved breathing patterns after the start of PN. F rotein administration also may influence ventilatory demand by increased ventilatory response to hypoxia and hypercapnia. This stimulation may be altered by the amino acid composition of the protein source, with increased amounts of BCAAs having a greater effect compared with standard amino acids." Although this protein effect is potentially beneficial in some patients, excessive protein administration could theoretically lead to increased work of breathing and fatigue." ... 

Chronic hypoxia (CH) from birth blunts the ventilatory response to hypoxia in rats (21) and other species by unknown mechanisms. Although CH alters the VE response to hypoxia at the central nervous system level (99), CH from birth also affects maturation of carotid body type I cell O2 sensitivity. Type I cells dissociated from 11-day-old rats reared from birth in Fi02 0.12 demonstrated marked blimting of [Ca ]i responses to acute hypoxia compared with controls reared in noimoxia... 

The relationship between ventilation and arterial P02 is relatively flat over the physiological range but substantial increases in ventilation do occur as hypoxia becomes more severe. The amount of variability in this response fi om species to species, however, is enormous. Much of this variabdity undoubtedly reflects adaptation to differing environmental, behavioral, or physiological demands. Thus the blunted hypoxic ventilatory responses seen in fossorial (burrowing) birds and mammals (7,8) are beheved to be an adaptation that minimizes the use of increased... 

Some patients lose the ability to increase the rate or depth or respiration in response to persistent hypoxemia. This decreased ventilatory drive may be due to abnormal peripheral or central respiratory receptor responses. This relative hypoventilation leads to hypercapnia in this situation the central respiratory response to a chronically increased PaC02 can be blunted. Because these changes in Pa02 and PaC02 are subtle and progress over many years, the pH is usually near normal because the kidneys compensate by retaining bicarbonate. 

Respiratory acidosis may produce neuromuscular symptoms, including altered mental status, abnormal behavior, seizures, stupor, and coma. Hypercapnia may mimic stroke or CNS tumors by producing headache, papilledema, focal paresis, and abnormal reflexes. Carbon dioxide acts as a vasodilator in the brain, thus causing an increase in cerebral blood flow. This increase in cerebral blood flow is thought to be partially responsible for the CNS symptoms. The CNS response to hypercapnia is extremely variable between patients and is also influenced by the acuity of presentation. Chronic hypercapnia blunts the usual respiratory stimulus resulting from increased PaC02. In patients with severe chronic respiratory acidosis, hypoxemia rather than hypercapnia provides the primary ventilatory stimulus. ... 

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