464133
Description
Flashcards by sophietevans, updated more than 1 year ago
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Created by sophietevans
almost 11 years ago
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| Question | Answer |
| What is the function of the dive response in aquatic mammals? | The dive response enables aquatic mammals to conserve oxygen by decreasing heart rate and blood flow to the extremities. |
| Given that oxygen consumption rises if terrestrial animals are placed in cold water, what is the function of the dive response in them? | In terrestrial animals, oxygen consumption actually rises as a result of submersion in cold water in order to prevent core temperature from dropping, so the bradycardia (resting HR <60BPM) and peripheral vessel constriction serve to keep blood in the trunk and help conserve heat. |
| In this lab, how did we stimulate the dive response in the subject? Which nerve receptors were stimulated? | In this lab, we triggered the dive response by suddenly submerging the subject’s face in cold water (~10°C), stimulating the trigeminal nerve receptors around the nose. |
| What is the relationship between the water temperature and bradycardia in the dive response? How is this achieved? | As water temperature decreases, stimulation of the receptors is enhanced, and the severity of the bradycardia increases. Enhanced stimulation of these receptors results in an inhibition of the cardiovascular centre, as well as subsequent reduction in heart rate through both enhanced parasympathetic output and reduced sympathetic output to the heart. |
| What is the difference between the physiological effects of the dive response and holding one's breath? | While the dive response initiates bradycardia and there are minimal O2/CO2 effects, breath-holding initiates tachycardia, hypoxia and hypercapnia. |
| When investigating the change in heart rate between the dive response and holding one's breath, what equipment was used? | A finger pulse transducer was attached to the middle finger of the subject and to a Powerlab panel was required for both, and a basin of icy water with a thermometer was required for the dive response. |
| By occluding the venous return in the thigh, what aspect of the dive response was being replicated? | In peripheral vessel constriction of the dive response, venous return to the heart is disrupted, but the amount returned is also reduced along with cardiac output. We replicated that by blocking venous return and then measuring the decrease in the volume of the calf when the cuff was removed (as the gradual increase could not be detected by the transducer, but the sudden decrease could). |
| What equipment was required to assess change in blood volume in peripheral occlusion? | A blood pressure cuff (inflated to 100mmHg) and sphygmomanometer were attached to the subject's thigh, a respiratory belt was attached to the same calf and the Powerlab panel, and the basin of cold water was used in the dive response. |
| What does an increased amplitude in the dive response suggest? | An increased stroke volume. |
| Why might tachycardia have occurred instead of bradycardia in the dive response? | The water may not have been cold enough to stimulate the receptors of the trigeminal nerve to increased parasympathetic activity to the heart, or the subject may have panicked after being submerged. |
| Why does the heart rate increase during breath holding? | The tissues are being starved of oxygen and the carbon dioxide produced during respiration is not being cleared, due to inadequate supply of oxygenated blood to the tissue. As the body cannot increase the PO2 of the blood arriving directly without ventilation and external respiration, it increases the volume of blood perfusing the tissue to attempt to supply the oxygen demand. |
| Why did the change in leg volume decrease in the dive response and increase during breath holding, when compared with vessel occlusion under resting conditions? | The lower change in the dive response is expected, as stroke volume is decreased so there is less blood to return to the heart, meaning that less will accumulate when return is occluded. In the breath-hold, there is increased cardiac output to address the tissue hypoxia, so there will be more blood to return to the heart, resulting in a larger accumulation when return is occluded. |
| Is the dive response a pathological presentation? | No, it is more of a survival mechanism. However, the circulatory effects of breath holding were clear, and could be similar in pathologies in which air flow and gaseous exchange is restricted, such as emphysema, pulmonary fibrosis, and asthma. |
| What can the dive response be used for clinically? | Clinically, the dive response can be used to restore sinus rhythm to those with paroxysmal supraventricular tachycardia. This can occur with digitalis toxicity, or in Wolff-Parkinson-White syndrome in which a person has an extra pathway for impulses to travel in the heart. |
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