COAST ELECTRONICS

METABOLIC MONITOR

The Metabolic Monitor is primarily intended to be used in studies of small quadripeds including ruminents (in conjunction with one of our methane analyzers).

VENTILATED FLOW-THROUGH CALORIMETRY

Various methods of collecting expired gas, employing flow-through systems, have been devised for the determination of metabolic gas exchange and energy expenditure in both man and animals.  Such techniques are convenient for purposes of indirect calorimetry wherever a degree of confinement of the test subject is acceptable.  The common underlying principle is that of forcing a stream of air to pass across the expiratory pathway of the subject at such a rate as to entrain the entire expirate.  At the same time, the test subject will be taking up oxygen from the fresh air stream supplied, and releasing carbon dioxide and water vapour into it.

There are three methods of accomplishing expired air collection, namely [1] via a mouthpiece or a face mask; [2] within a hood or canopy positioned over the head or the upper body; and [3] from a totally enclosing body chamber which has discrete inlet and outlet ports.  The measurement of gas exchange and of energy expenditure requires accurate knowledge of the air flow which bathes the subject and of the difference in concentration between the incoming air value and the outgoing value of each of the respiratory gases of interest, principally oxygen, carbon dioxide and water.

The relationship of the forced flow rate to the-subject's level of ventilation is of considerable importance in the flow-through technique, as is the size of the hood, canopy or chamber which encompasses the subject. Flexibility of use is assured if the appropriate size of chamber or hood is selected to accommodate the subject, and the flow rate adjusted accordingly within the constraints of the measuring system.

This form of indirect calorimetry demands gas analysers of enhanced sensitivity and stability. They need an order of magnitude greater performance than that afforded by conventional analysers for purposes of respiratory measurement. The attainment of accurate differential readings [comparing a stable reference with the sampled gas] requires meticulous attention to calibration and continual checks against reliable standards.

The open-circuit chamber method has been widely used for the measurement of energy expenditure in animals of agricultural importance, and in man.

The ventilated hood method is an alternative that has similarly been extensively employed in human and animal studies. A canopy, which may be constructed of perspex, some form of plastic material or polythene, covers the head, upper part of the body or forequarters, or the whole body. Air is drawn into the hood either through a designated inlet or through the interstices of the hood as it invests the body of the test subject. The requisite negative pressure is created by a turbine or pump that is sited well downstream, and the air flow should be sufficient to entrain the expired air in its entirety.  Energy expenditure can be measured successfully in animals over extended periods by this method.

The use of a mouthpiece [and noseclip], face mask or endotracheal tube constitutes a third method of flow-through metabolic measurement.  This fitting should be attached by insertion into a continuously flowing air stream into, and from, which the subject breathes.

All of those calorimetric techniques which depend on flow-through ventilation have the requirement (a) that the entire expirate of the test subject should be entrained, and (b) that the level of ventilation should be geared to exceed the expiratory flow by a factor of 4 to 10 or, in general terms, set at a rate of flow equivalent to the body mass in kilogrammes expressed in litre.min-1.  It should further be borne in mind that the optimal measuring range of the gas analysers is 0 - 1 percent in differential terms, and that this span and its resolution have been chosen in cognisance of the physiological effects on the control of respiration which follow a rise in inspiratory carbon dioxide to above the 1 percent level.

The use of a mixing chamber is strongly recommended in the interests of the complete homogenisation of the expirate with the ventilatory stream.  Where a sizeable enclosure such as a cabin is employed, a mixing fan will also be desirable, and in this context too, the effects of dead space ventilation may need to be taken into account.

SPECIFICATIONS

SYSTEM CONTROLLER

Processor Type: 8-bit Microcontroller

Display: 40 x 2 line backlit Super-Twist Liquid Crystal

Functions:                                           Calculation and display of: Ventilation Flow Rate,

                                                     Gas Exchange Variables [V02, VCO2 and RER],

                                                     Metabolic Energy Expenditure [ME], in addition to

                                                     general functional parameters and Calibration Data

• Control and averaging of C02 Analyser Carrier
• Control and calculation of Analyser time-sharing for differential gas measurement by means of Driving of gas sample multiplexing solenoids at set time intervals, and the reading / averaging of Analyser output signals at the appropriate times.

Analogue Outputs:

                                     Range:0 to +4.096V (+5V if overranged)

• 02 signal; 2 V/l% 02
• C02 signal: 2 V/1% C02
• C02 signal: 2 V/1% C02
• CH₄ signal: 1 V/1% CH₄
• Flow: 1 V /litre /min

 

• Serial Link: RS232 protocol at baud rate of 9600 bit /s with use of CTS handshaking. 1 start, 1 or 2 stops, no parity

TEMPERATURE SENSOR

Measurement Range: 0 to 100oC

Accuracy: Typically 0.5oC

 

FLOW METER /CONTROLLER

 

• Measuring Principle:                      Differential Pressure Pneumotachometry employing
• -2 to +2 cm H20 temperature-stabilised piezo-     resistive  transducer in  conjunction with an unheated No.2 size  Fleisch-type pneumotachograph
• Flow Controller Principle: Flow meter output is utilised in the production of a closed-loop PWM [pulse width modulated] control system for purposes of stable through-ventilation

 

Measurement Range:                 0 to 190 litre. Min (3 litres/sec)

Flow Resolution: 0.1 litre.

Flow Control Range: Definable from 25 to 190 litre/min

 

• Flow Control Regulation: Feedback from transducer inlet pressure sensing:
• Typically achieves a restoration of flow [at nominal baseline ventilation level of 100 litre.min^-1 to within 2 litre. min-1 of baseline] per cm H20 sensed reduction in inlet pressure. Regulation effective to a maximum reduction of 4 cm H20 in inlet pressure.
• Flow Meter Zero Drift: 0.75 % [=1.5 L. min^-1 over 200 L. min^-1 range] during 8 hours at constant temperature
• Flow Meter Span Drift: 2 % of reading over 8 hours at constant temperature

 

OXYGEN ANALYSER

• Measuring Principle: Single compact heated zirconia cell analyser adapted for differential analysis by means of fixed-interval time-sharing between sample and reference gas. [See System Controller]
• Absolute Range: 0 to 25 percent Oxygen Concentration
• Differential Range: Reference or Sample Gas Input [Centred at 20.9 %]:
• Maximum 02 Concentration = 22.9 %
• Minimum 02 Concentration = 18.9 %
• i.e. Measurement Range cf. 20.9 % = +2 % to -2 %     Measurement Range cf 21.9% +1 % to -3 %
• Absolute Drift: Zero: 0.1 % 02 in 8 hours at constant temperature
• Span: 0.005 % 02 per 8 h at constant temperature
• Differential Drift: Zero: 0.002%O2

 Span: Directly proportional to absolute span drift

  with specified constant flow rate

 

• Differential Zero Stability: 0.002 % 02
• Note: For purposes of checking differential 02 Zero, both gas inputs should be connected to, and sampling the same stable source gas [normally fresh room air] which is being drawn through a mixing volume.

 

CARBON DIOXIDE ANALYSER

 

• Measuring Principle: Single-Beam Non-Dispersive Infrared [NDIR] Analyser with differential gas measurement and auto-zeroing routines effected through fixed-interval
• time-sharing.  [See System Controller]

 

• Absolute Range: 0 to 2 % C02 Concentration
• Differential Range: Reference or Sample Gas Input:
• Maximum C02 Concentration = 2.0 % Minimum C02 Concentration =0 %
• i.e. Measurement Range cf .05 % = +1.95 / -0.05 %
• Measurement Range cf. .50 % = +1.50 / -0.50 %
• AbsoluteDnft: Zero: 0.003%CO2

 Span: 0.003 % C02

DifferentialDnft: Zero: 0.002%O2

 Span: Directly proportional to absolute span drift

  with specified constant flow rate

 

• Differential Zero Stability: 0.002 % C02
• Note: For purposes of checking differential C02 Zero, both gas inputs should be connected to, and sampling the same stable source gas [normally fresh room air] which is being drawn through a mixing volume.

SYSTEM POWER SUPPLY

 

• Supply Voltage: Nominally 100 to 120 V.A.C. or 200 to 240 VAC. Appropriate range selectable on IEC mains inlet.
• Power Requirement: 30 VA
• Fuse Rating: For 100 to 120 V.A.C.: T 160mA /250 V

 For 200 to 240 VAC.: T 315mA /250 V

Operating Frequency: 47 to 63 Hz

 

MECHANICAL SPECIFICATIONS

Weight 7 kg Approx.

Dimensions: 190 x 390 x 160mm

Operating Temperature Range: 10 to 40 0C