Mechanics of ventilation in swellsharks, Cephaloscyllium ventriosum (Scyliorhinidae). (1/238)

A simple two-pump model has served to describe the mechanics of ventilation in cartilaginous and bony fishes since the pioneering work of G. M. Hughes. A hallmark of this model is that water flow over the gills is continuous. Studies of feeding kinematics in the swellshark Cephaloscyllium ventriosum, however, suggested that a flow reversal occurred during prey capture and transport. Given that feeding is often considered to be simply an exaggeration of the kinematic events performed during respiration, I investigated whether flow reversals are potentially present during respiration. Pressure and impedance data were coupled with kinematic data from high-speed video footage and dye studies and used to infer patterns of water flow through the heads of respiring swellsharks. Swellsharks were implanted with pressure transducers to determine the pattern and magnitude of pressures generated within the buccal and parabranchial (gill) cavities during respiration. Pressure traces revealed extended periods of pressure reversal during the respiratory cycle. Further, impedance data suggested that pressures within the buccal and parabranchial cavities were not generated by the cyclic opening and closing of the jaws and gills in the manner previously suggested by Hughes. Thus, the classic model needs to be re-evaluated to determine its general applicability. Two alternative models for pressure patterns and their mechanism of generation during respiration are provided. The first depicts a double-reversal scenario common in the swellshark whereby pressures are reversed following both of the pump stages (the suction pump and the pressure pump) rather than after the pressure-pump stage only. The second model describes a scenario in which the suction pump is insufficient for generating a positive pressure differential across the gills; thus, a pressure reversal persists throughout this phase of respiration. Kinematic analysis based on high-speed video footage and dye studies, however, suggested that during respiration, as opposed to feeding, distinct flow reversals do not result from the pressure reversals. Thus, water is probably pooling around the gill filaments during the long periods of pressure reversal.  (+info)

Dominant frequency content of ocular microtremor from normal subjects. (2/238)

Ocular microtremor (OMT) is a high frequency tremor of the eyes present during fixation and probably related to brainstem activity (Coakley, D. (1983). Minute eye movement and brain stem function. CRC Press, FL.). Published observations on the frequency of OMT have varied widely. Ocular microtremor was recorded in 105 normal healthy subjects using the Piezoelectric strain gauge technique. The dominant frequency content of a signal was determined using the peak counting method. Values recorded ranged from 70 to 103 Hz, the mean frequency being 83.68 Hz (S.D. +/- 5.78 Hz).  (+info)

Automated measurement of oxygen consumption by the yellow fever mosquito, Aedes aegypti. (3/238)

Oxygen consumption of single mosquitoes was measured using a differential pressure transducer (DPT) connected to two small chambers. A mosquito was placed in the experimental chamber (P1) and was separated from NaOH by 4 cm2 of marquisette mesh. The reference chamber (P2) contained the same amount of NaOH and the marquisette mesh but without a mosquito. When these two chambers were sealed, removed O2 from P1 resulted in a pressure decrease with respect to P2. This pressure differential was transduced into an output voltage that was directly proportional to the amount of O2 consumed by the mosquito. An array of eight DPTs was interfaced with an IBM 486 PC using an ADAC 5500MF analog to digital converter and software from ADAC (Direct View) to automate the recording procedure. We determined that our apparatus was sensitive enough to detect subtle differences in O2 consumption in mosquitoes subjected to different physiologic conditions.  (+info)

Cheek and tongue pressures in the molar areas and the atmospheric pressure in the palatal vault in young adults. (4/238)

The pressures acting on the maxillary and mandibular posterior teeth from the tongue and cheeks were measured in 24 adults aged 22-29 years. In addition, the pressure in the palatal vault was recorded. The pressure at two maxillary (buccal and lingual) and two mandibular (buccal and lingual) measuring points, and in the palatal vault was recorded simultaneously. Repeated recordings of the pressures at rest, and during chewing and swallowing were made. The pressures at rest were of similar magnitude (about 2 g/cm2) at the buccal and lingual sides of the mandibular posterior teeth. The median resting pressure at the maxillary posterior teeth was 2.7 g/cm2 on the buccal side and 1.0 g/cm2 on the lingual side. The difference in the maxilla was significant, but not in the mandible. It was concluded that the equilibrium of tooth position is maintained by the pressure from the cheeks and the tongue. During chewing and swallowing the pressures on the lingual side of the teeth were greater than those on the buccal side. At rest about half of the subjects had a negative pressure at the palatal vault, but no correlations between the resting pressure at the palatal vault and the resting pressures on the teeth were found.  (+info)

An in vivo comparison of a catheter mounted pressure transducer system with conventional balloon catheters. (5/238)

In the assessment of respiratory muscle function balloon catheters have been widely used for pressure measurements. However, this type of investigation is poorly tolerated by acutely ill patients. This study assessed the performance of a possible alternative, a catheter-mounted miniature pressure transducer (CMT). The assessment consisted of a laboratory study of the linearity, frequency response, and stability of gain and baseline of the CMT system, and an in vivo study directly comparing the CMT and balloon catheter systems in seven normal subjects for a range of respiratory manoeuvres. These were: 1) maximal inspiratory and expiratory pressures against a closed airway, 2) twitch transdiaphragmatic pressure elicited by cervical magnetic phrenic nerve stimulation, and 3) tidal breathing, sniffs and coughs in five body positions. The agreement of the two systems was analysed for measurements of 1) absolute pressures, 2) magnitude of changes in pressure, and 3) rate of change of pressure (maximum relaxation rate after sniff manoeuvres). The CMT system was linear, with a high frequency response and stable gain, but showed baseline drift. The two systems agreed well for measurements of change and rate of change of pressure, but less well for measurements of absolute pressure. The CMT system tested is potentially useful for studies of acute changes in respiratory pressures, or studies of respiratory muscle strength, but would be less useful where accurate measurements of absolute pressures are required.  (+info)

Effect of co-activation of tongue protrudor and retractor muscles on tongue movements and pharyngeal airflow mechanics in the rat. (6/238)

1. The purpose of these experiments was to examine the mechanisms by which either co-activation or independent activation of tongue protrudor and retractor muscles influence upper airway flow mechanics. We studied the influence of selective hypoglossal (XIIth) nerve stimulation on tongue movements and flow mechanics in anaesthetized rats that were prepared with an isolated upper airway. In this preparation, both nasal and oral flow pathways are available. 2. Inspiratory flow limitation was achieved by rapidly lowering hypopharyngeal pressure (Php) with a vacuum pump, and the maximal rate of flow (VI,max) and the nasopharyngeal pressure associated with flow limitation (Pcrit) were measured. These experimental trials were repeated while nerve branches innervating tongue protrudor (genioglossus; medial XIIth nerve branch) and retractor (hyoglossus and styloglossus; lateral XIIth nerve branch) muscles were stimulated either simultaneously or independently at frequencies ranging from 20-100 Hz. Co-activating the protrudor and retractor muscles produced tongue retraction, whereas independently activating the genioglossus resulted in tongue protrusion. 3. Co-activation of tongue protrudor and retractor muscles increased VI, max (peak increase 44 %, P < 0.05), made Pcrit more negative (peak decrease of 44 %, P < 0.05), and did not change upstream nasopharyngeal resistance (Rn). Independent protrudor muscle stimulation increased VI,max (peak increase 61 %, P < 0.05), did not change Pcrit, and decreased Rn (peak decrease of 41 %, P < 0.05). Independent retractor muscle stimulation did not significantly alter flow mechanics. Changes in Pcrit and VI,max at all stimulation frequencies were significantly correlated during co-activation of protrudor and retractor muscles (r2 = 0.63, P < 0.05), but not during independent protrudor muscle stimulation (r2 = 0.09). 4. These findings indicate that either co-activation of protrudor and retractor muscles or independent activation of protrudor muscles can improve upper airway flow mechanics, although the underlying mechanisms are different. We suggest that co-activation decreases pharyngeal collapsibility but does not dilate the pharyngeal airway. In contrast, unopposed tongue protrusion dilates the oropharynx, but has a minimal effect on pharyngeal airway collapsibility.  (+info)

Time-dependent pressure distortion in a catheter-transducer system: correction by fast flush. (7/238)

BACKGROUND: Distortion of the pressure wave by a liquid-filled catheter-transducer system leads most often to an overestimation in systolic arterial blood pressure in pulmonary and systemic circulations. The pressure distortion depends on the catheter-transducer frequency response. Many monitoring systems use either mechanical or electronic filters to reduce this distortion. Such filters assume, however, that the catheter-transducer frequency response does not change over time. The current study aimed to study the changes with time of the catheter-transducer frequency response and design a flush procedure to reverse these changes back to baseline. METHODS: An in vitro setup was devised to assess the catheter-transducer frequency response in conditions approximating some of those met in a clinical environment (slow flushing, 37 degrees C, 48-h test). Several flush protocols were assessed. RESULTS: Within 48 h, catheter-transducer natural frequency decreased from 17.89 +/- 0.36 (mean +/- SD) to 7.35 +/- 0.25 Hz, and the catheter-transducer damping coefficient increased from 0.234 +/- 0.004 to 0.356 +/- 0.010. Slow and rapid flushing by the flush device built into the pressure transducer did not correct these changes, which were reversed only by manual fast flush of the transducer and of the catheter. These changes and parallel changes in catheter-transducer compliance may be explained by bubbles inside the catheter-transducer. CONCLUSIONS: Catheter-transducer-induced blood pressure distortion changes with time. This change may be reversed by a manual fast flush or "rocket flush" procedure, allowing a con. stant correction by a filter.  (+info)

Popliteal vein entrapment: a benign venographic feature or a pathologic entity? (8/238)

PURPOSE: Asymptomatic morphologic popliteal vein entrapment is frequently found in the healthy population (27%). In our institution, popliteal vein compression on plantar flexion was observed in 42% of all ascending venograms. Some authorities consider the lesion benign, without pathologic significance. This study examines the pathophysiologic importance in select patients, describes treatment with surgery, and suggests a diagnostic tool. METHOD: Thirty severely symptomatic patients with venographic evidence of popliteal entrapment were selected to have popliteal vein release after a process of elimination (ie, other causes of chronic venous insufficiency [CVI] were ruled out by means of comprehensive hemodynamic and morphologic studies). In the last nine limbs, popliteal vein pressure was also measured by means of the introduction of a 2F transducer tip catheter. Patients were clinically and hemodynamically assessed before and after surgery, and anatomical anomalies encountered during surgery were recorded. RESULTS: Popliteal vein release was performed without mortality or serious morbidity. Anomalies of the medial head of the gastrocnemius muscle caused entrapment in 60% of the patients; anatomic course venous anomalies were infrequent (7% of the patients). Significant relief of pain and swelling occurred in the patients who had surgery. Stasis ulceration/dermatitis resolved in 82% of patients. Popliteal venous pressures had normalized in the six patients who were studied postoperatively. CONCLUSION: Popliteal vein entrapment should be included in the differential diagnosis of CVI in patients in whom other, more common etiologies have been excluded on the basis of comprehensive investigations. Popliteal vein compression can be demonstrated venographically in a large proportion of patients with CVI, but the lesion is likely pathological only in a small fraction of these patients. A technique for popliteal venous pressure measurement is described; it shows promise as a test for functional assessment of entrapment. Immediate results of popliteal vein release surgery are encouraging; long-term follow-up is necessary to judge the efficacy of surgical lysis of entrapment in symptomatic patients who fail to improve with conservative treatment measures.  (+info)