Pharmacological manipulation of human gastrointestinal blood flow

Smoking prevents the expected postprandial increase in intestinal blood flow: a Doppler sonographic study

OBJECTIVE

To assess whether cigarette smoking had an effect on superior mesenteric artery postprandial blood flow.

METHODS

Forty-six subjects were studied in 3 groups with Doppler sonography. Group A consisted of nonsmokers; groups B and C consisted of smokers. In group B, subjects were allowed to smoke cigarettes postprandially, whereas in group C, postprandial smoking was prohibited. A baseline Doppler evaluation was performed in the fasting state, and consecutive Doppler evaluations were performed postprandially with 30-min intervals for 120 minutes. Doppler sonographic measurements of the superior mesenteric artery, including peak systolic and end-diastolic velocities, resistive index, and diameter, were calculated. Statistical analysis was performed by analysis of variance.

RESULTS

All groups showed significant changes with time for all parameters (P < .001 for all). The changes in time were significantly different at 90 and 120 minutes for peak systolic velocity, at 90 minutes for end-diastolic velocity, and at 120 minutes for diameter between groups. Group B had the greatest differences. Compared with group A, changes in peak systolic velocity at 90 to 120 minutes were significantly lower in group B (P = .007 and .006, respectively), and compared with groups A and C, changes in end-diastolic velocity at 90 minutes (P = .006 and .004, respectively) and diameter at 120 minutes (P = .007 and .011, respectively) were significantly lower in group B.

CONCLUSIONS

Smoking immediately after meals was associated with a superior mesenteric artery blood flow increase that was lower than expected, which may explain the belief that smoking reduces body weight. Postprandial smoking may have undesired results in patients with chronic intestinal ischemia.

The effects of dietary nucleotides on intestinal blood flow in preterm infants

Nucleotides (NT) are reported to affect development of the immune and gastrointestinal systems, and they are currently added to most term infant formulas. In the present study, dietary NT effects on superior mesenteric artery blood flow were investigated. Formula-fed preterm infants were studied once with a 20 kcal/oz. term infant formula containing 80.6 mg/L of NT (NT+), and once with the same formula with no added NT (NT-) (n = 20, gestational age 28.0 +/- 2.2 wk). A reference group of preterm infants fed human milk was also studied (n = 20, gestational age 29.0 +/- 1.6 wk). Superior mesenteric artery blood flow velocities (BFV) were measured by Doppler ultrasound 15 min before and 30, 60, and 90 min after the start of the feed. BFV rose in all infants from baseline to 30 min after feed initiation, and progressively declined thereafter in infants fed NT- or human milk. However, NT+ feedings were associated with a minimal change in BFV between 60 and 90 min. As a result, the difference in blood flow velocities between baseline and 90 min was significantly greater with the NT+ versus the NT- feedings for the mean, peak systolic, and end diastolic velocities (p = 0.03, 0.05, and 0.03, respectively). BFV after the NT- and human milk feedings were similar. These data suggest that orally administered NT are associated with effects on the intestinal vasculature.

Understanding gastrointestinal perfusion in critical care: so near, and yet so far

An association between abnormal gastrointestinal perfusion and critical illness has been suggested for a number of years. Much of the data to support this idea comes from studies using gastric tonometry. Although an attractive technology, the interpretation of tonometry data is complex. Furthermore, current understanding of the physiology of gastrointestinal perfusion in health and disease is incomplete. This review considers critically the striking clinical data and basic physiological investigations that support a key role for gastrointestinal hypoperfusion in initiating and/or perpetuating critical disease.