Blood pressure in the tarantula,Dugesiella hentzi

Summary

• 1. Heart rates in intact spiders at rest were 35/min and after 3 min exercise 77/min. Recovery to the initial rate required 1/2 hr. In cannulated animals heart rates ranged from 44/min at rest to 116/min after a struggle. Heart rate was relatively independent of internal pressure.

• 2. Variations in heart rate and amplitude occurred spontaneously and in response to various stimuli (Fig. 6).

• 3. Systole averages 68% of total beat duration through a range of heart rates from 21–116 min (Fig. 4).

• 4. Intraventricular pressures 10 min after cannulating averaged 22/13 mm Hg, but fell to 12/8 mm Hg after 10 min in the dark (Fig. 5). A maximum pressure of 102 mm Hg was measured in one animal. The pressure recorded in the heart is generated in part by the heart and in part reflects abdominal tension.

• 5. Resting pressures in any 2 legs were always identical and were above that in the prosoma.

• 6. Resting pressures in the prosoma and lateral sacs are intermediate to heart systolic and diastolic pressures which in a relaxed animal were 12/8 mm Hg (Fig. 11).

• 7. At rest a gradient of only a few mm Hg propels the blood through the lung books from the lateral sacs to the pulmonary veins; a gradient of 1–2 mm Hg exists between the pulmonary vein and the heart in diastole.

• 8. General abdominal pressure is above pulmonary vein pressure suggesting a need for a mechanism to maintain patency of these vessels.

• 9. During a struggle a maximum pressure of 480 mm Hg was measured in the prosoma.

• 10. High pressures were recorded in the lateral sacs which communicate freely with the prosoma but were not transmitted to the heart.

• 11. Pressures of 40–60 mm Hg were measured in the prosoma and legs during wialking (Fig. 18) and delivery of blood through the pedal arteries probably continues at this level.

• 12. Withdrawal of blood causes an immediate decrease in heart pressure. Within min some recovery occurs presumably because of muscular adjustments (Fig. 19).