Massimo Ferrigno

Deadly diving? Physiological and behavioural management of decompression stress in diving mammals

Decompression sickness (DCS; ‘the bends’) is a disease associated with gas uptake at pressure. The basic pathology and cause are relatively well known to human divers. Breath-hold diving marine mammals were thought to be relatively immune to DCS owing to multiple anatomical, physiological and behavioural adaptations that reduce nitrogen gas (N2) loading during dives. However, recent observations have shown that gas bubbles may form and tissue injury may occur in marine mammals under certain circumstances. Gas kinetic models based on measured time-depth profiles further suggest the potential occurrence of high blood and tissue N2 tensions. We review evidence for gas-bubble incidence in marine mammal tissues and discuss the theory behind gas loading and bubble formation. We suggest that diving mammals vary their physiological responses according to multiple stressors, and that the perspective on marine mammal diving physiology should change from simply minimizing N2 loading to management of the N2 load. This suggests several avenues for further study, ranging from the effects of gas bubbles at molecular, cellular and organ function levels, to comparative studies relating the presence/absence of gas bubbles to diving behaviour. Technological advances in imaging and remote instrumentation are likely to advance this field in coming years.

Utilization of Arterial Blood Gas Measurements in a Large Tertiary Care Hospital

We describe the patterns of utilization of arterial blood gas (ABG) tests in a large tertiary care hospital. To our knowledge, no hospital-wide analysis of ABG test utilization has been published. We analyzed 491 ABG tests performed during 24 two-hour intervals, representative of different staff shifts throughout the 7-day week. The clinician ordering each ABG test was asked to fill out a utilization survey. The most common reasons for requesting an ABG test were changes in ventilator settings (27.6%), respiratory events (26.4%), and routine (25.7%). Of the results, approximately 79% were expected, and a change in patient management (eg, a change in ventilator settings) occurred in 42% of cases. Many ABG tests were ordered as part of a clinical routine or to monitor parameters that can be assessed clinically or through less invasive testing. Implementation of practice guidelines may prove useful in controlling test utilization and in decreasing costs.

Static inflation and deflation pressure-volume curves from excised lungs of marine mammals.

SUMMARY Excised lungs from eight marine mammal species [harp seal (Pagophilus groenlandicus), harbor seal (Phoca vitulina), gray seal (Halichoerus grypush), Atlantic white-sided dolphin (Lagenorhynchus acutus), common dolphin (Delphinus delphis), Rissos dolphin (Grampus griseus), long-finned pilot whale (Globicephala melas) and harbor porpoise (Phocoena phocoena)] were used to determine the minimum air volume of the relaxed lung (MAV, N=15), the elastic properties (pressure–volume curves, N=24) of the respiratory system and the total lung capacity (TLC). Our data indicate that mass-specific TLC (sTLC, l kg–1) does not differ between species or groups (odontocete vs phocid) and agree with that estimated (TLCest) from body mass (Mb) by applying the equation: TLCest=0.135 Mb0.92. Measured MAV was on average 7% of TLC, with a range from 0 to 16%. The pressure–volume curves were similar among species on inflation but diverged during deflation in phocids in comparison with odontocetes. These differences provide a structural basis for observed species differences in the depth at which lungs collapse and gas exchange ceases.

Early Healing of Transcolonic and Transgastric Natural Orifice Transluminal Endoscopic Surgery Access Sites

BACKGROUND Natural Orifice Transluminal Endoscopic Surgery (NOTES) is a developing, minimally invasive surgical approach whose potential benefits are being investigated. Little is known about secure access site closure and early healing kinetics of transvisceral access. STUDY DESIGN Transvisceral access incisions were created in the colon (C-NOTES, n = 8) and stomach (G-NOTES, n = 8) for peritoneal exploration. Incisions were closed primarily with endoloops, endoclips, or t-tags. Macroscopic and histologic analyses performed on postoperative day 7 assessed gross appearance, granulation tissue, inflammation, ulceration, and complications. RESULTS Macroscopically, incisions appeared closed without intraperitoneal spillage. Incisions closed by endoloop and t-tags showed intense granulation tissue fill of defect despite partial (G-NOTES, n = 3) and transmural ulceration (C-NOTES, n = 8; G-NOTES, n = 3). Of the 30 t-tags applied, 40% broke or deployed into the peritoneal cavity. Endoclip closures (C-NOTES, n = 1; G-NOTES, n = 1) did not show histologic mucosal continuity. Healing complications included transmural necrosis (C-NOTES, n = 1; G-NOTES, n = 1), foreign body material (C-NOTES, n = 3; G-NOTES, n = 2), and microabscesses (G-NOTES, n = 1). CONCLUSIONS This study provides a reproducible model to assess noninvasive repair of planned visceral perforations. Of investigated technologies, endoloop closure was favored for transcolonic incisions, and t-tags with omental patch for transgastric incisions, although these have significant limitations. Endoclips were inadequate for primary closure, but may be useful as an adjunctive closure modality. Additional studies are needed to examine visceral repair at later time points, as they will help determine the quality and kinetics of repair of a variety of incision closure strategies. This study demonstrates the need for improved technologies to more reliably close visceral transluminal defects.

A fluoroscopic and laryngoscopic study of glossopharyngeal insufflation and exsufflation.

Glossopharyngeal breathing, frequently performed by elite breath-hold divers, relies on muscles of the mouth and pharynx to move air into (glossopharyngeal insufflation, GI) and out of the lungs (glossopharyngeal exsufflation, GE). GI has also been used by patients with weak respiratory muscles. Fluoroscopic and endoscopic examinations were performed on four divers (three of whom were world record holders) during both GI and GE maneuvers. A detailed pictorial description of both GI and GE, with online video material that includes external, endoscopic and fluoroscopic examinations, is provided in this publication. Both GI and GE are accomplished with a coordinated series of contractions by glossopharyngeal muscles and they rely on a piston pump-like action of the larynx. In particular, the larynx moves extensively and repeatedly up and down, to either inject air into (GI) or extract it from the lungs (GE), with the vocal cords functioning as a valve. During both maneuvers, when the larynx is in its highest position, the epiglottis does not fold back, unlike what happens during swallowing.

“Ventilatory alternans”: A left–right alternation of inspiratory airflow in humans

In a study visualizing ventilation with hyperpolarized (3)He magnetic resonance imaging (MRI) in elite breath hold divers, the dynamic MRI images in one subject exhibited an apparent alternation of the image intensity between left and right lung. We hypothesized that the alternation resulted from alternating variations in inspiratory flow rate to left and right lungs. Analysis showed that the alternation was not due to random uncorrelated temporal fluctuations of intensity (p<0.001). The frequency of alternation was approximately 56 min(-1), suggesting a cardiac origin. Similar alternation of ventilation was confirmed retrospectively in 4 of 6 additional subjects. These observations are consistent with previous studies showing cardiogenic mixing of gas in the lung. We speculate that cardiogenic pendelluft, possibly from ballistic lateral motion of the beating heart, could cause alternating variations of inspiratory flow to the lungs.

Inhalation heterogeneity from subresidual volumes in elite divers

Punctate reopening of the lung from subresidual volumes (sub-RV) is commonly observed in excised lung preparations, either degassed or collapsed to zero transpulmonary pressure, and in the course of reinflation of human lungs when the chest is open, secondary to traumatic or surgical pneumothoraxes. In the course of physiological studies on two elite breath-hold divers, who are able to achieve lung volumes well below traditional RV with glossopharyngeal exsufflation, we used MRI lung imaging with inhaled hyperpolarized (129)Xe to visualize ventilatory patterns. We observed strikingly inhomogeneous inhalation patterns with small inhalation volumes from sub-RV, consistent with reopening of frankly closed airways. On the other hand, two age-matched and two older controls, inhaling from just above RV, showed a much more homogeneous pattern. Our results demonstrate the concept of frank airway closure below RV in young healthy adults with an intact chest wall.

High blood pressure during breath-hold diving is not a physiological absurdity

to the editor: In a 2009 article, Sieber et al. ([4][1]), having found “normal” blood pressures (BPs) using a sphygmomanometric method in subjects performing breath-hold dives to 10 m of depth, suggested that the very high BPs we recorded invasively in two healthy expert breath-hold divers

Extending submarine crew survival by reducing CO2 production with quickly reversible sedation.

INTRODUCTION CO2 accumulation may limit crew survival in a disabled submarine. Reversible sedation using diazepam and flumazenil was proposed to reduce CO2 production. METHODS Two groups of three resting subjects were studied during a 48-h placebo phase with diazepam and flumazenil placebos, followed by a 48-h drug phase with oral diazepam to induce sedation and intranasal flumazenil to reverse it. CO2 exchange was measured every 2.5 h; twice a day, cognitive testing and meals were preceded by placebo or flumazenil. Return to sedated state was produced with either placebo or diazepam. In the drug phase, initial diazepam doses (10 to 40 mg) were followed by maintenance doses to achieve sedation corresponding to Alertness Scores of 3 or 4. RESULTS In the drug phase, subjects received a total of 360-495 mg of diazepam (with doses of 5-40 mg), average alertness score was 3.75, and mean Vco2 was 14% less than in the placebo phase (0.212 vs. 0.248 L x min(-)). Subjects were 21-36% less active when sedated with diazepam. The mean flumazenil dose to restore full alertness was 0.36 mg, with subjects being conversant and oriented within 5 min, performing cognitive tasks at 86-97% of their baseline. Subjects could follow instructions and ambulate independently, though unsteadily 6 h after final flumazenil dose; at 72 h they exhibited normal cognitive and physical functions. DISCUSSION Reversible sedation to lower crew metabolism in a disabled submarine may be effective, safe, and practical.

Marked pericardial inhomogeneity of specific ventilation at total lung capacity and beyond

We measured regional ventilation at 1l above functional residual capacity (FRC+1L) and total lung capacity (TLC) in three normal subjects and four elite breath-hold divers, and above TLC after glossopharyngeal insufflation (TLC+GI) in the divers. Hyperpolarized (3)He MRI was used to map the local ventilation per unit volume over the entire lung. At TLC and above, there was markedly increased regional ventilation of the lungs in the pericardial region compared with the relatively uniform ventilation throughout the rest of the lung. The distribution of fractional ventilation regionally was relatively uniform at FRC+1L, with a small non-gravitational cephalocaudal gradient of specific ventilation in the supine posture. Our observations at high lung volumes are consistent with the effect of high pleural tension in the concave pericardial region, which promotes expansion of the subjacent lung, leading to a higher local effective compliance and a higher specific ventilation.