<Observation xmlns="http://hl7.org/fhir">
    <id value="demo-obs-pef-4" />
    <status value="final" />
    <code>
        <coding>
            <system value="http://loinc.org" />
            <code value="19935-6" />
            <display value="Maximum expiratory gas flow Respiratory system airway by Peak flow meter" />
        </coding>
    </code>
    <subject>
        <reference value="Patient/demo-patient-1" />
    </subject>
    <effectiveDateTime value="2018-03-21" />
    <valueQuantity>
        <value value="302" />
        <system value="http://unitsofmeasure.org" />
        <code value="L/min" />
    </valueQuantity>
    <referenceRange>
        <low>
            <value value="346" />
            <system value="http://unitsofmeasure.org" />
            <code value="L/min" />
        </low>
        <text value="Personal best peak flow 432 L/min" />
    </referenceRange>
</Observation>