We investigated the regional distribution of blood flow (Q) within the costal and crural portions of the diaphragm in a total of eight anesthetized supine mongrel dogs. Q was measured with 15-microns microspheres, radiolabeled with three different isotopes, injected into the left ventricle during spontaneous breathing (SB), inspiratory resistive loading (IR), and mechanical ventilation after paralysis (P). At necropsy, the costal and crural portions of each hemidiaphragm were arbitrarily subdivided along a sagittal plane into five to seven and three sections, respectively. During P, there was a dorsoventral Q gradient within the costal part of the diaphragm. During SB there was a fourfold increase in the gradient of Q. Furthermore, during IR, in which mouth pressures of -16 +/- 4 cmH2O were generated, there was a further increase in the gradient of Q. During both SB and IR, Q to the most ventral portion of the costal diaphragm was 26 +/- 6% less than the peak value. In two dogs, studied prone and supine, there was no difference in the Q gradients between the two postures. Over the dorsal 80% of the costal diaphragm there was also a dorsoventral gradient of muscle thickness, such that the most dorsal part was 54 +/- 2% (n = 5) that of the ventral portion. In contrast, there was no consistent gradient of Q or muscle thickness within the crural diaphragm. Our results demonstrate a topographical gravity-independent distribution of Q in the costal, but not the crural, diaphragm.(ABSTRACT TRUNCATED AT 250 WORDS)

The overriding principle of military surgery is the delayed primary suture of wounds. Therefore. by definition, battle casualties will receive more than one anaesthetic for the treatment of their injuries. The use of the Triservice anaesthetic apparatus (TSA) has bccii well tried and documented.',' It is a drawover system that uses ambient air iis the primary carrier gas, and halothane and trichlorocthylcnc a the volatile anaesthetic agcnts.However, in view of current opinions about liver damage due 10 repeated halothane it would be prcferablc if this agent were no1 used in the first instance. In addition, the manufacture of trichloroethylene has been threatened in the past and the future production of this agent cannot be guaranteed. The use of the newer inhalational agents, entlurane and isoflurane. has been rec o n~m c n d c d .~ Unfortunately. enflurane, which does have analgesic p r o p e r t i~s .~ has a high MAC and isoflurane, at present. is very expensive.We felt that ;I total intravenous technique is an obvious altcrnative in the treatment of battle casualties. This study was therefore designed to assess the suitability of such a technique using a mixture that contained ketamine, niidamlarn and vecuronium, ;iccuratcly dclivered intravenously by ineans of a syringe pump. Ketaminc has becn uscd widely as the induction and maintenance drug of choice for trauma cases but the high incidence of unpleasant side effects has limited its acceptance. Vecuronium bromide, one of the rnore recently introduced non-depolarising muscle relaxants. has been used because it is available as an anhydrous powder and therelhre stores well. Vccuronium is frcc of advcrsc circulatory effects and the incidence of release of histamine is minirnal.'j It is our contention that all battle casualties will have a full stomach, irrespective of the interviil between timc of injury and time of surgery. Therefore, tracheal intubation is mandatory and intermittent positive pressure venlilation can be iiscd for the duration of the surgical procedure. Another essential recluiremcnt for w x surgery is (hat patients should recover quickly and be able to maintain clear airway as soon as possible. MrriiorliOne hundred patients, 36 male and 64 Ccmale. age range 16-50 years. who presented for elective abdominal, thoracic or body surface surgery at this hospital wcre studied. All patients were in ASA classes 1 and 2. It MBS estimated that their operations would last at least 45 minutes. Patients with a past medical history of psychiatric illness. with hypertension and those with a history of ;I previous ccrcbrovascular iiccidcnt wcrc not studied. All patients were seen prc-operativcly. Thc following details were recorded: initials, sex, body weight. relevant medical history and physical findings. All were prcnicdicated with papavereturn and hyoscinc one hour preoperatively. Monitoring of the electrocardiogram a n d blood pressure (Dinamap) wis commenced on arrival in the anaesthetic room and a vein on thc dorsiun of the hand or forearm was cannulate...

In awake supine normal subjects, dimensional changes of the oropharyngeal airway were measured during exposure to negative intraluminal pressures. The pressure was generated 1) "actively" by subjects inspiring against an externally occluded airway or 2) "passively" by external suction at the mouth during voluntary glottic closure with no inspiratory effort. Airway dimensions were imaged with X-ray fluoroscopy and anteroposterior diameters measured at levels corresponding to cervical vertebra 3 and 4 (C3 and C4). Cephalad axial displacement of the hyoid bone (CDHY) was also measured. During the "active" maneuver, airway diameters and position were maintained at resting levels despite airway pressure up to -15 cmH2O. In contrast, during the passive maneuver at -15 cmH2O, C3 was only 15 +/- 9% and C4 only 47 +/- 8% of control; CDHY was 5.6 +/- 1.8 mm. In three subjects airway wall apposition occurred and persisted until an active inspiratory effort. We conclude that, in the absence of inspiratory effort, negative oropharyngeal airway pressures result in marked narrowing and cephalad displacement of the upper airway, even during wakefulness. Therefore, our data suggest that the complex interaction of upper airway and thoracic muscle activity is critical in determining the effective compliance and patency of the upper airway, which is readily collapsible even in normal subjects.

We addressed the question whether gravity-dependent differences in passive tension and length of the diaphragm are associated with differences in its regional activation. By using intramuscular electrodes, we measured the electromyographic activity of different parts of the diaphragm (Edi) during quiet breathing in several postures in 13 anesthetized mongrel dogs. The Edi of the left and right costal hemi-diaphragm was compared between the left and right lateral decubitus postures, whereas that from the substernal and crural regions was compared between the supine and prone positions. On changing posture, the Edi of the dependent part of the diaphragm decreased in both cases, whereas that of the non-dependent part increased. The results were consistent with reflex modulation of regional diaphragm activation in response to postural changes in local resting length. However, these changes in Edi persisted after bilateral vagotomy, cordotomy (C7-T1) and dorsal rhizotomy of the C5-C7 roots. Compound muscle action potentials, recorded in different regions of the diaphragm and evoked by supramaximal stimulation of the phrenic nerves, were altered with changes in posture in the same direction as Edi. Because the stimuli were supramaximal, these changes reflected systematic changes in the recording conditions with posture, possibly because of a combination of 1) changes in the electrical environment surrounding the intramuscular electrodes and 2) passive changes in muscle length. Our results demonstrate systematic, reproducible, posture-dependent changes in regional Edi that may not be due to different neural drive.(ABSTRACT TRUNCATED AT 250 WORDS)

Summary Two low‐volume, variable performance oxygen delivery Systems were compared in conscious spontaneously breathing volunteers. Oropharyngeal oxygen concentrations were measured during periods of nose and mouth breathing. The Systems were studied at oxygen flow rates of 2 or 4 litres/minute. The performance of both Systems was similar under the test conditions but the nasal catheter is preferable in terms of cost.